全文获取类型
收费全文 | 19219篇 |
免费 | 2147篇 |
国内免费 | 1670篇 |
专业分类
化学 | 4749篇 |
晶体学 | 53篇 |
力学 | 1233篇 |
综合类 | 296篇 |
数学 | 8933篇 |
物理学 | 3534篇 |
无线电 | 4238篇 |
出版年
2024年 | 42篇 |
2023年 | 223篇 |
2022年 | 289篇 |
2021年 | 439篇 |
2020年 | 527篇 |
2019年 | 523篇 |
2018年 | 497篇 |
2017年 | 590篇 |
2016年 | 744篇 |
2015年 | 605篇 |
2014年 | 1035篇 |
2013年 | 1560篇 |
2012年 | 1033篇 |
2011年 | 1169篇 |
2010年 | 1033篇 |
2009年 | 1186篇 |
2008年 | 1237篇 |
2007年 | 1287篇 |
2006年 | 1134篇 |
2005年 | 953篇 |
2004年 | 884篇 |
2003年 | 834篇 |
2002年 | 772篇 |
2001年 | 637篇 |
2000年 | 622篇 |
1999年 | 467篇 |
1998年 | 428篇 |
1997年 | 352篇 |
1996年 | 329篇 |
1995年 | 297篇 |
1994年 | 220篇 |
1993年 | 193篇 |
1992年 | 164篇 |
1991年 | 141篇 |
1990年 | 87篇 |
1989年 | 66篇 |
1988年 | 63篇 |
1987年 | 48篇 |
1986年 | 51篇 |
1985年 | 45篇 |
1984年 | 46篇 |
1983年 | 21篇 |
1982年 | 21篇 |
1981年 | 27篇 |
1980年 | 22篇 |
1979年 | 26篇 |
1978年 | 18篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
1.
2.
《Indagationes Mathematicae》2021,32(6):1229-1239
3.
G. Peruginelli 《代数通讯》2018,46(11):4724-4738
We classify the maximal subrings of the ring of n×n matrices over a finite field, and show that these subrings may be divided into three types. We also describe all of the maximal subrings of a finite semisimple ring, and categorize them into two classes. As an application of these results, we calculate the covering number of a finite semisimple ring. 相似文献
4.
Most notable Kinetoplastids are of the genus Trypanosoma and Leishmania, affecting several millions of humans in Africa and Latin America. Current therapeutic options are limited by several drawbacks, hence the need to develop more efficacious inhibitors. An investigation to decipher the mechanism behind greater inhibitory potency of a chroman-4-one derivative (compound 1) in Trypanosoma brucei pteridine reductase 1 (TbPTR1) and Leishmania major pteridine reductase 1 (LmPTR1) was performed. Estimation of ΔGbind revealed that compound 1 had a greater binding affinity in TbPTR1 with a ΔGbind value of −49.0507 Kcal/mol than −29.2292 Kcal/mol in LmPTR1. The ΔGbind in TbPTR1 were predominantly contributed by “strong” electrostatic energy compared to the “weak” van der Waals in LmPTR1. In addition to this, the NADPH cofactor contributed significantly to the total energy of TbPTR1. A characteristic weak aromatic π interaction common in PTR1 was more prominent in TbPTR1 than LmPTR1. The consistent occurrence of high-affinity conventional hydrogen bond interactions as well as a steady interaction of crucial active site residues like Arg14/Arg17, Ser95/Ser111, Phe97/Phe113 in TbPTR1/LmPTR1 with chroman-4-one moiety equally revealed the important role the moiety played in the activity of compound 1. Overall, the structural and conformational analysis of the active site residues in TbPTR1 revealed them to be more rigid than LmPTR1. This could be the mechanism of interaction TbPTR1 employs in exerting a greater potency than LmPTR1. These findings will further give insight that will be assistive in modifying compound 1 for better potency and the design of novel inhibitors of PTR1. 相似文献
5.
对复杂高阶系统进行模型简化,为研究与设计系统提供了方便的条件。对系统模型的降阶是控制系统设计与仿真工作者的一个重要研究课题,对高阶复杂系统的分析、设计、仿真等具有重要的理论意义和工程实用价值。针对目前比较成熟的基于系统矩阵的有序实Schur分解方法,提出了采用时矩输出拟合来改善降阶系统输出响应逼近程度的改进方法,从而使简化模型具有输出误差更小、计算简便等优点,通过给出的实例仿真证实了这一点。 相似文献
6.
7.
8.
As we approach 100 nm technology the interconnect issues are becoming one of the main concerns in the testing of gigahertz system-on-chips. Voltage distortion (noise) and delay violations (skew) contribute to the signal integrity loss and ultimately functional error, performance degradation and reliability problems. In this paper, we first define a model for integrity faults on the high-speed interconnects. Then, we present a BIST-based test methodology that includes two special cells to detect and measure noise and skew occurring on the interconnects of the gigahertz system-on-chips. Using an inexpensive test architecture the integrity information accumulated by these special cells can be scanned out for final test and reliability analysis. 相似文献
9.
In this paper, we study the existence of the uniformly minimum risk equivariant (UMRE) estimators of parameters in a class
of normal linear models, which include the normal variance components model, the growth curve model, the extended growth curve
model, and the seemingly unrelated regression equations model, and so on. The necessary and sufficient conditions are given
for the existence of UMRE estimators of the estimable linear functions of regression coefficients, the covariance matrixV and (trV)α, where α > 0 is known, in the models under an affine group of transformations for quadratic losses and matrix losses, respectively.
Under the (extended) growth curve model and the seemingly unrelated regression equations model, the conclusions given in literature
for estimating regression coefficients can be derived by applying the general results in this paper, and the sufficient conditions
for non-existence of UMRE estimators ofV and tr(V) are expanded to be necessary and sufficient conditions. In addition, the necessary and sufficient conditions that there
exist UMRE estimators of parameters in the variance components model are obtained for the first time. 相似文献
10.