全文获取类型
收费全文 | 4844篇 |
免费 | 282篇 |
国内免费 | 90篇 |
专业分类
测绘学 | 181篇 |
大气科学 | 461篇 |
地球物理 | 1170篇 |
地质学 | 1616篇 |
海洋学 | 398篇 |
天文学 | 831篇 |
综合类 | 18篇 |
自然地理 | 541篇 |
出版年
2023年 | 19篇 |
2022年 | 25篇 |
2021年 | 101篇 |
2020年 | 114篇 |
2019年 | 113篇 |
2018年 | 176篇 |
2017年 | 172篇 |
2016年 | 216篇 |
2015年 | 184篇 |
2014年 | 206篇 |
2013年 | 355篇 |
2012年 | 216篇 |
2011年 | 280篇 |
2010年 | 225篇 |
2009年 | 265篇 |
2008年 | 257篇 |
2007年 | 260篇 |
2006年 | 232篇 |
2005年 | 190篇 |
2004年 | 175篇 |
2003年 | 154篇 |
2002年 | 146篇 |
2001年 | 102篇 |
2000年 | 112篇 |
1999年 | 85篇 |
1998年 | 64篇 |
1997年 | 62篇 |
1996年 | 53篇 |
1995年 | 46篇 |
1994年 | 39篇 |
1993年 | 35篇 |
1992年 | 30篇 |
1991年 | 35篇 |
1990年 | 29篇 |
1989年 | 41篇 |
1988年 | 19篇 |
1987年 | 29篇 |
1986年 | 26篇 |
1985年 | 41篇 |
1984年 | 28篇 |
1983年 | 28篇 |
1982年 | 20篇 |
1981年 | 28篇 |
1980年 | 22篇 |
1979年 | 22篇 |
1978年 | 18篇 |
1977年 | 16篇 |
1976年 | 12篇 |
1974年 | 12篇 |
1973年 | 11篇 |
排序方式: 共有5216条查询结果,搜索用时 15 毫秒
51.
A theoretical and an experimental investigation was carried out, where a carbon fibre corrugated circular cylinder was tested to destuction under external hydrostatic pressure. The theoretical investigation was via the finite element method, where the structure was modelled with several orthotropic axisymmetric thin-walled shell elements. The experimental observations were aided with strategically placed strain gauges. Comparison between theory and experiment showed that the experimentally observed buckling pressure was a little lower than the theoretical prediction. This may have been due to the fact that the model had slight initial geometrical imperfections in the circumferenential direction. 相似文献
52.
53.
The complexation of dissolved Ni has been evaluated in a rapidly-flushed, rural estuary (Tweed, UK) by ligand exchange-adsorptive cathodic stripping voltammetry. Results suggest the presence of strongly binding ligands, L, throughout, with average stability constants of about 1019 and which are saturated by ambient Ni concentrations. Equilibrium speciation calculations incorporating these constants in WHAM, version 6, predict an increase in Ni complexation (as NiL) from about 50% of total dissolved Ni in fresh water to over 90% in sea water. Equivalent calculations using the default-mode fulvic and humic substances (FS and HS, respectively) encoded in the WHAM database predict a reduction in complexation (as NiFS + NiHS) from about 20% in fresh water to less than 1% in sea water. Discrepancies arising from the two approaches are largely attributed to the different analytical detection windows employed. Thus, a better representation of Ni complexation is derived from including both types of complexant in the speciation calculations, resulting in estimates of net complexation in excess of 60% of total dissolved Ni throughout the estuary. The uncertainties and assumptions inherent in all computations illustrate the difficulty in measuring or predicting metal complexation in estuaries. 相似文献
54.
55.
Toshiro Saino Alexander Bychkov Chen-Tung Arthur Chen Paul J. Harrison 《Journal of Oceanography》2004,60(1):1-4
This special issue is comprised of 13 papers, including this overview, and focuses on the synthesis of the Joint Global Ocean
Flux Study (JGOFS) in the North Pacific which took place from 1997 through 2003. The effort was led by the JGOFS North Pacific
Synthesis Group, with the aim of quantifying CO2 drawdown by physical and biological pumps in the North Pacific by identifying and studying the regional, seasonal to inter-annual
variations in the key processes, and understanding their regulating mechanisms. Emphasis was placed on the similarities and
differences of the biogeochemical regimes in the eastern and western subarctic Pacific. Effort was also made to address the
future research directions which arose from the scientific findings during the North Pacific JGOFS process study. A brief
overview of the papers from view points of CO2 drawdown by physical and biological pumps, spatial variability, and temporal variability from seasonal to decadal scales
is made, followed by suggestions for the directions of future research.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
56.
Nicholas H. Vrolijk Nancy M. Targett Bruce R. Woodin John J. Stegeman 《Marine environmental research》1995,39(1-4)
The relationship between cytochrome P450 and feeding on terpenoid-rich gorgonian corals was investigated in a species of tropical butterflyfish and compared with two other sympatric congeners that do not feed on gorgonians. Fish were collected from non-polluted waters in Belize and the levels of two cytochrome P450 isozymes (CYP2B and CYP3A) were immunoquantitated in addition to quantification of total P450. Chaetodon capistratus regularly feeds on gorgonian corals and has higher levels of total hepatic microsomal cytochrome P450 than C. ocellatus or C. striatus. The content of hepatic P450 (0.588–0.794 nmol mg−1) in C. capistratus is among the highest ever reported in teleosts from non-polluted waters and is significantly greater than detected in C. ocellatus or C. striatus. Chaetodon capistratus also had a larger hepatic index (g liver per g fish) and more microsomal protein (mg protein per g liver), factors that translate into 3.3- to 8-fold more total P450 per g fish. Sexual differences in total P450 were observed between male and female C. capistratus, but not among the other species. The contents of proteins detected by immunoassay with polyclonal anti-scup P450B (CYP2B) and anti-human P4503A (CYP3A) were 2- to 10-fold and 2- to 20-fold greater, respectively, in C. capistratus than in the congeneric species. CYP2 and CYP3 gene families in mammals are thought to have evolved partially in response to dietary allelochemicals. These results suggest that these P450 isozymes may also be important in marine teleosts that feed on terpenoid-rich prey. 相似文献
57.
58.
59.
The paper describes experimental tests carried out on three ring-stiffened cones that were tested to destruction under external hydrostatic pressure. The cones were carefully machined from EN1A Steel. All three cones failed by plastic non-symmetric bifurcation buckling in a mode commonly known as general instability. In this mode the entire ring-shell combination buckles bodily.The paper also provides a design chart using the results obtained from these three vessels, together with the results of six other vessels obtained from other tests. The design chart allows the possibility of obtaining a plastic knock down factor, so that the theoretical buckling pressures, based on elastic theory, can be divided by the plastic knockdown factor, to give the predicted buckling pressure. This method can also be used for the design of full-scale vessels. 相似文献
60.
Lynne D. Talley Pavel Tishchenko Vladimir Luchin Alexander Nedashkovskiy Sergey Sagalaev Dong-Jin Kang Mark Warner Dong-Ha Min 《Progress in Oceanography》2004,61(2-4):277
Hydrographic properties from CTD and discrete bottle sample profiles covering the Japan (East) Sea in summer, 1999, are presented in vertical sections, maps at standard depths, maps on isopycnal surfaces, and as property–property distributions. This data set covers most of the Sea with the exception of the western boundary region and northern Tatar Strait, and includes nutrients, pH, alkalinity, and chlorofluorocarbons, as well as the usual temperature, salinity, and oxygen observations. 相似文献