全文获取类型
收费全文 | 6707篇 |
免费 | 681篇 |
国内免费 | 458篇 |
专业分类
化学 | 4945篇 |
晶体学 | 74篇 |
力学 | 359篇 |
综合类 | 38篇 |
数学 | 745篇 |
物理学 | 1685篇 |
出版年
2024年 | 15篇 |
2023年 | 82篇 |
2022年 | 204篇 |
2021年 | 244篇 |
2020年 | 208篇 |
2019年 | 233篇 |
2018年 | 206篇 |
2017年 | 179篇 |
2016年 | 297篇 |
2015年 | 248篇 |
2014年 | 304篇 |
2013年 | 512篇 |
2012年 | 470篇 |
2011年 | 516篇 |
2010年 | 327篇 |
2009年 | 316篇 |
2008年 | 353篇 |
2007年 | 335篇 |
2006年 | 323篇 |
2005年 | 234篇 |
2004年 | 222篇 |
2003年 | 202篇 |
2002年 | 236篇 |
2001年 | 171篇 |
2000年 | 151篇 |
1999年 | 127篇 |
1998年 | 117篇 |
1997年 | 102篇 |
1996年 | 75篇 |
1995年 | 91篇 |
1994年 | 82篇 |
1993年 | 61篇 |
1992年 | 63篇 |
1991年 | 50篇 |
1990年 | 50篇 |
1989年 | 31篇 |
1988年 | 27篇 |
1987年 | 27篇 |
1986年 | 36篇 |
1985年 | 46篇 |
1984年 | 35篇 |
1983年 | 34篇 |
1982年 | 29篇 |
1981年 | 25篇 |
1980年 | 17篇 |
1979年 | 18篇 |
1977年 | 13篇 |
1975年 | 12篇 |
1974年 | 11篇 |
1973年 | 12篇 |
排序方式: 共有7846条查询结果,搜索用时 15 毫秒
21.
22.
Anhua Wan 《Journal of Applied Mathematics and Computing》2005,19(1-2):345-351
An effective method for analyzing the stability of nonlinear systems is developed. After introducing a novel concept named the point-wise generalized Dahlquist constant for any mapping and presenting its useful properties, we show that the point-wise generalized Dahlquist constant is sufficient for characterizing the exponential stability of nonlinear systems. 相似文献
23.
Numerical schemes for systems with multiple spatio-temporal scales are investigated. The multiscale schemes use asymptotic results for this type of systems which guarantee the existence of an effective dynamics for some suitably defined modes varying slowly on the largest scales. The multiscale schemes are analyzed in general, then illustrated on a specific example of a moderately large deterministic system displaying chaotic behavior due to Lorenz. Issues like consistency, accuracy, and efficiency are discussed in detail. The role of possible hidden slow variables as well as additional effects arising on the diffusive time-scale are also investigated. As a byproduct we obtain a rather complete characterization of the effective dynamics in Lorenz model. 相似文献
24.
Mat Rasol Awang Hassan Hamdani Mutaat Mohd. Shukri Mahmud Wan Badrin Wan Husain Tajuddin Osman Khomsaton Abu Bakar Asmahwati Kassim Zal U''yun Wan Mahmud Ishak ManafTamikazu Kume Shoji Hashimoto 《Radiation Physics and Chemistry》1993,42(4-6):611-616
In solid state fermentation, Pleurotus sajor-caju has been found to be able to degrade at least 30% oil palm empty Fruit Bunch (EFB) fibre leaving 70 % useful materials. Conditions under which fermentation carried out were investigated. It was found that, in the temperature range between 25– 28 °C, relative ph between 6–8, moisture between 60–70 % and medium composition of CaCO3: rice bran 2 %: 5 % were the optimum conditions. The results showed in fermented products that, there were substantial reduction in cellulosic component such as Crude Fiber (CF, 18 %); Acid Detergent Fibre (ADF, 45 %), Neutral Detergent Fibre (NDF, 61 %) and Acid Detergent Lignin (ADL, 14 %). However, Crude Protein (CP, 10%) increased resulted from single cell protein enrichment of mycelial microbial mass. The mass reductions of substrate in fermentation process corresponds to the CO2 released during fermentation. Hence, attributable to the decreased in content of CF, ADF, NDF, and ADL. The digestibility study has also been carried out to determine the useful level of this product to ruminant. Aflatoxin content was detected low in both the initial substrates and products. Based on nutritional value and low content of aflatoxin, the product is useful as a source of roughage to ruminant. 相似文献
25.
26.
描述了一种延长EPR波谱仪中速调管使用寿命的方法.根据这种方法,只要正确地调谐微波桥的工作状态和适当地调整功率电平器的功率校正电平.即使对于已经严重老化的速调管仍然可以继续使用一段时间,维持仪器的正常运行. 相似文献
27.
We give several equivalent characterisations of left (and hence, by duality, also of right) supported algebras. These characterisations are in terms of properties of the left and the right parts of the module category, or in terms of the classes L0 and R0 which consist respectively of the predecessors of the projective modules, and of the successors of the injective modules. 相似文献
28.
在Linux操作平台下应用FAST_wmg有限元前后处理软件对机械密封焊接金属波纹管膜片建立了有限元模型并进行了非线性有限元分析.在同等条件下对焊接金属波纹管采用了S型膜片和V型膜片,并分别进行了有限元强度评价和对比分析.结果表明,两种膜片最大应力集中都在膜片两端周围发生.这与文献所叙述的波纹管的主要失效发生在膜片两端与焊谷接近的部位非常吻合,但是,在同样边界条件下,在同样位移量时S型膜片最大应力值比V型膜片最大应力值小,压缩量大. 相似文献
29.
Nanocrystalline FeS2 cathode material of lithium cell was synthesized from cheap materials of FeSO4, Na2S2O3, and sulfur by a hydrothermal process. The scanning electron microscopy analysis showed the obtained material was nano-sized,
about 500 nm. The X-ray powder diffraction analysis showed that the synthetic FeS2 material had two phases of the crystalline structure, pyrite and marcasite. The phase of marcasite seems to have no negative
effect on the electrochemical performance of the material. The synthetic FeS2 showed a significant improvement of electrochemical performance for Li/FeS2 cells. 相似文献
30.