全文获取类型
收费全文 | 1157篇 |
免费 | 168篇 |
国内免费 | 243篇 |
专业分类
测绘学 | 94篇 |
大气科学 | 284篇 |
地球物理 | 286篇 |
地质学 | 484篇 |
海洋学 | 142篇 |
天文学 | 52篇 |
综合类 | 112篇 |
自然地理 | 114篇 |
出版年
2024年 | 6篇 |
2023年 | 29篇 |
2022年 | 48篇 |
2021年 | 65篇 |
2020年 | 40篇 |
2019年 | 51篇 |
2018年 | 51篇 |
2017年 | 54篇 |
2016年 | 61篇 |
2015年 | 47篇 |
2014年 | 56篇 |
2013年 | 68篇 |
2012年 | 40篇 |
2011年 | 64篇 |
2010年 | 61篇 |
2009年 | 63篇 |
2008年 | 61篇 |
2007年 | 60篇 |
2006年 | 30篇 |
2005年 | 36篇 |
2004年 | 26篇 |
2003年 | 29篇 |
2002年 | 46篇 |
2001年 | 41篇 |
2000年 | 29篇 |
1999年 | 64篇 |
1998年 | 52篇 |
1997年 | 44篇 |
1996年 | 32篇 |
1995年 | 32篇 |
1994年 | 28篇 |
1993年 | 26篇 |
1992年 | 24篇 |
1991年 | 15篇 |
1990年 | 19篇 |
1989年 | 17篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1970年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1568条查询结果,搜索用时 15 毫秒
991.
文章对1998年长江流域二度梅雨期西太平洋副热带高压的活动与大气经圈环流的关系进行了分析。结果指出,副高的进退与经圈环流的调整有着密切的关系。副高的北跳并不是由与其相联系的反环流下沉支直接北移所引起的。低纬度深厚上升运动的发展不利于副高维持在较低的纬度,而中纬度反环流的突然向南调整则有利于副高在更北的纬度建立,于是副高出现突然北跳的现象。它是江淮地区出梅的一种经圈环流调整形式。副高在稳定期间,随着与它相联系的反环流的南北运动而作相应的南北运动。副高在南退之前,对流层顶附近有反环流生成,然后迅速向南运动,副高也随之迅速南退。 相似文献
992.
There are abundant bitumens and oil seepages stored in vugs in a Lower-Triassic Daye formation (T1d) marlite in Ni’erguan village in the Southern Guizhou Depression. However, the source of those oil seepages has not been determined to date. Multiple suites of source rocks of different ages exist in the depression. Both the oil seepages and potential source rocks have undergone complicated secondary alterations, which have added to the difficulty of an oil-source correlation. For example, the main source rock, a Lower-Cambrian Niutitang Formation (?1n) mudstone, is over mature, and other potential source rocks, both from the Permian and the Triassic, are still in the oil window. In addition, the T1d oil seepages underwent a large amount of biodegradation. To minimize the influence of biodegradation and thermal maturation, special methods were employed in this oil-source correlation study. These methods included catalytic hydropyrolysis, to release covalently bound biomarkers from the over mature kerogen of ?1n mudstone, sequential extraction, to obtain chloroform bitumen A and chloroform bitumen C from the T1d marlite, and anhydrous pyrolysis, to release pyrolysates from the kerogen of T1d marlite. Using the methods above, the biomarkers and n-alkanes released from the oil samples and source rocks were analysed by GC–MS and GC-C-IRMS. The oil-source correlation indicated that the T1d oil seepage primarily originated from the ?1n mudstone and was partially mixed with oil generated from the T1d marlite. Furthermore, the seepage also demonstrated that the above methods were effective for the complicated oil-source correlation in the Southern Guizhou Depression. 相似文献
993.
994.
995.
利用贵州省2011—2015年10个太阳辐射站观测资料,采用最小二乘法分月拟合太阳辐射计算参数a、b,结合相应站点的地理信息(纬度和海拔高度),建立参数随地理位置变化的分月模型,进行1962—1990年威宁站独立样本检验,利用2001—2010年贵阳站数据与海拔分区法进行比较;结合1981—2010年85个常规气象站日照时数资料和相应站点的地理信息推算累年各月太阳总辐射量,并探讨其空间分布规律。结果表明:用分月参数模型计算贵州省太阳辐射误差更小、精度更高,提高了太阳辐射计算的准确率;贵州省气象台站年平均太阳总辐射在3415.76~4737.04 MJ·m~(-2)之间,西部和西南部多,北部少,其中年总辐射最大值出现在威宁,最低值出现在务川。 相似文献
996.
A three-dimensional(3D) global adiabatic spectral primitive equation model has been designed.The main features are as follows.(1) Adoption of spherical harmonics and Tschebyscheff polynomials as the basis functions in the horizontal and vertical respectively,but the unknowns in the spectral equations are two-dimensional;(2) Inclusion of the tropopause,which may vary with time and space;(3) Suggestion of a spectral method for representing the vertical structure of the atmosphere applicable to the unsmoothed profile case;(4) In consideration of nonlinear vertical aliasing a technique is proposed to avoid it and nonlinear computational instability.Based on real data forecasts up to 48 hours have been performed.The results show that the statistical verifications with the model are superior on the average to those with the T42L9 used operationally before 1995 at NMC of China at the same mean resolution. 相似文献
997.
初筛表明,一株分离自北极加拿大海盆海冰心芯样品的海单胞菌(Marinomonas sp.BSi20584)具有较高的β-D-半乳糖苷酶活性,为了研究清楚其酶学性质,将经hiTAIL-PCR扩增得到的β-D-半乳糖苷酶基因(galt)与pET-28a(+)原核表达载体结合,转入大肠杆菌BL21(DE3)。经IPTG诱导后对重组β-D-半乳糖苷酶(GALT)的表达条件进行了优化,采用金属螯合亲和层析技术制备纯酶,并对重组GALT的酶学性质进行了研究。结果显示,重组酶的最适诱导温度为20℃,在IPTG浓度为0.07mmol/L时诱导22h后,酶活和产酶量达到最大值。GALT单体分子量约为6.6×104 g/mol,天然酶为同源三聚体。GALT最适作用温度为35℃,其热稳定性较好,在60℃处理5h后,仍可保持50%以上的相对活性。GALT的最适作用pH为9.0,在pH为6.0~11.0范围内比较稳定。GALT的最适NaCl浓度为0.5mol/L,对盐度具有较高的耐受性。Mg2+、K+、DTT和EDTA对酶活不具有显著影响,而Mn2+、Fe2+对酶活有促进作用,Zn2+和L-谷胱甘肽对酶活有抑制作用。GALT对Galβ1-4GlcNAc具有水解作用,而对Galβ1-3GalNAc和Galβ1-3GlcNAc糖苷键型没有水解能力。本研究实现了海单胞菌属菌株的β-D-半乳糖苷酶基因在大肠杆菌系统中的高效表达,并系统研究了重组酶的酶学特性,为后续开展该酶的代谢适应性和潜在应用研究提供详细的酶学数据基础。 相似文献
998.
999.
Shi-Yong Liao Yao-Hui Jiang Shao-Yong Jiang Wan-Zhi Yang Qing Zhou Guo-Dong Jin Peng Zhao 《Mineralogy and Petrology》2010,100(1-2):55-74
This paper presents detailed SHRIMP zircon U–Pb chronology, mineral chemistry, major and trace element, and Sr–Nd–Hf isotope geochemistry of the Datong pluton and its quenched enclaves from the western Kunlun orogen, northwest China, in an attempt to achieve a better understanding on the origin of diverse arc magmas. The Datong host granitoids are intermediate to acid in composition (SiO2?=?57.5?~?73.1 wt.%), and exhibit high-K calc-alkaline to shoshonitic affinities. The quenched enclaves are silica-rich ultrapotassic rocks. Detailed SHRIMP zircon U–Pb dating indicates that the Datong pluton was emplaced in Ordovician time (473.4–447.7 Ma), which places the Datong pluton in an active continental margin setting, rather than a syn-collision setting of Early Silurian age. The Datong host granitoids were derived by partial melting of subducted sediments, with the subsequent melt interacting with the overlying mantle wedge during its ascent. Partial melting of the veined mantle wedge hybridized by sediment-derived melts generated the silica-rich ultrapotassic magma, which was injected into the Datong granitoid magma chamber and quenched, resulting in enclaves hosted by granitoids. This contribution provides evidence that arc magmas can be derived directly by partial melting of subducted sediments, which is helpful to further understand the origin of diverse arc magmas. 相似文献
1000.
卤虫繁殖机制的研究——Ⅰ.卵子发育过程中染色体的变化 总被引:1,自引:0,他引:1
本文以卤虫的生殖细胞卵子作为材料进行染色体标本制备,具体研究了卤虫卵子在发育过程中染色体的变化,探讨致使孤雌生殖卤虫染色体自然加倍的可能途径,以及两性生殖卤虫卵子发生受精的具体地点。 相似文献