全文获取类型
收费全文 | 6573篇 |
免费 | 1122篇 |
国内免费 | 1820篇 |
专业分类
测绘学 | 716篇 |
大气科学 | 1284篇 |
地球物理 | 1493篇 |
地质学 | 3254篇 |
海洋学 | 1075篇 |
天文学 | 174篇 |
综合类 | 598篇 |
自然地理 | 921篇 |
出版年
2024年 | 25篇 |
2023年 | 93篇 |
2022年 | 205篇 |
2021年 | 286篇 |
2020年 | 177篇 |
2019年 | 282篇 |
2018年 | 299篇 |
2017年 | 253篇 |
2016年 | 349篇 |
2015年 | 310篇 |
2014年 | 396篇 |
2013年 | 411篇 |
2012年 | 452篇 |
2011年 | 451篇 |
2010年 | 430篇 |
2009年 | 432篇 |
2008年 | 399篇 |
2007年 | 450篇 |
2006年 | 365篇 |
2005年 | 367篇 |
2004年 | 343篇 |
2003年 | 274篇 |
2002年 | 407篇 |
2001年 | 355篇 |
2000年 | 304篇 |
1999年 | 258篇 |
1998年 | 159篇 |
1997年 | 165篇 |
1996年 | 120篇 |
1995年 | 133篇 |
1994年 | 118篇 |
1993年 | 81篇 |
1992年 | 79篇 |
1991年 | 58篇 |
1990年 | 50篇 |
1989年 | 31篇 |
1988年 | 36篇 |
1987年 | 24篇 |
1986年 | 22篇 |
1985年 | 11篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1958年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有9515条查询结果,搜索用时 15 毫秒
61.
研究流形上的聚类分析,针对基于密度的空间聚类引入了流形概念,提出1种基于流形的密度聚类算法,该方法将流形的概念与聚类相结合,可以适用于样本为复杂分布的聚类。文中通过实例证明此算法的有效性。 相似文献
62.
Evaluation of bending moments and shear forces at unit connections of very large floating structures using hydroelastic and rigid body analyses 总被引:1,自引:0,他引:1
Byoung Wan Kim Sa Young Hong Jo Hyun Kyoung Seok Kyu Cho 《Ocean Engineering》2007,34(11-12):1668-1679
This paper investigates the characteristics of bending moments, shear forces and stresses at unit connections of very large floating structures (VLFS) under wave loads. The responses of VLFS are calculated by solving multi-body motion equation considering hydroelasticity and connection stiffness. Hydroelastic responses are calculated by the direct method. Higher-order boundary element method (HOBEM) is used for fluid analysis and finite element method (FEM) is introduced for structural analysis. The equation of motion is modified to describe the unit connections by employing spring elements. Bending moments and shear forces at the connections are obtained from the dynamic equilibrium condition for pressures and inertia forces. Two types of VLFS units such as tandem arranged units and side-by-side arranged units are considered in the numerical examples. The influences of connection stiffness, wave frequency and heading angle on responses of VLFS are investigated through the numerical examples. Rigid body analysis along with hydroelastic analysis is also carried out in the numerical analysis and comparison of those two approaches is discussed. 相似文献
63.
This paper presents a numerical model study of the propagation of water waves using the parabolic approximation of the mild-slope equation in the orthogonal coordinate system. Two types of coordinate systems are studied: (a) a general form of orthogonal coordinate system and (b) the conformal system, a special form of orthogonal coordinate system. Two typical examples, namely, expanded breakwaters and a circular channel, are studied to validate the model. First, the examples are studied by use of the general orthogonal coordinates. Then the same examples are computed by use of the confonnal system. The computational results show that the confonnal coordinate system generally gives better predictions than the general orthogonal system. A numerical technique for generating the conformal grid is combined with the numerical model to improve the practicability of the model. The comparison between the result from the numerical grid system and that from the analytical grid system shows that reliable computational results can be obtained by use of the numerical confonnal grid system. 相似文献
64.
65.
66.
67.
为了研究甘糖酯对大鼠体内尿激酶型纤溶酶原激活物 (urokinase PlasminogenActivator,u PA)活性的影响 ,采用溶解圈中和抑制法和发色底物法检测了大鼠口服甘糖酯后体内u PA活性的变化情况。结果表明 :甘糖酯可提高大鼠体内血液的纤溶活性 ,主要表现为 u PA活性升高。以不同剂量的甘糖酯连续喂药 10 d后 ,发现喂药组大鼠 u PA活性明显高于对照组 ,喂药组大鼠血浆 u PA活性升高同喂药剂量正相关 ,在 0~ 10 0 mg/ kg的剂量范围内 ,随喂药剂量增加而升高。提示在一定的剂量范围内甘糖酯可提高大鼠体内 u PA活性 ,激活纤溶系统 ,提高血液纤溶活性 ,表现出良好的抗栓作用 相似文献
68.
69.
70.
rmIoxThe averag annual dischaIge of the Zhujiang Xiver is 3. 32 x l0ll m3, which ranks theZhujiang River just end to the Changjiang River in China. The dischnye occutring duringthe fltal m between APril and ffepteTnber accounts for 80% of the yearly total. The Zhu-jiang hiver has a yeaIy sediment load of about 1 x l08 tons, which also concentrates in theM arn (Zhao, l990; Chen et al., 1998). The Zhujiang Xiver delta,which has l2 cities ofdifferent sizes and more than 40 towns with a po… 相似文献