全文获取类型
收费全文 | 15679篇 |
免费 | 1445篇 |
国内免费 | 580篇 |
专业分类
化学 | 5140篇 |
晶体学 | 27篇 |
力学 | 1145篇 |
综合类 | 36篇 |
数学 | 5258篇 |
物理学 | 2009篇 |
综合类 | 4089篇 |
出版年
2023年 | 159篇 |
2022年 | 153篇 |
2021年 | 243篇 |
2020年 | 434篇 |
2019年 | 333篇 |
2018年 | 305篇 |
2017年 | 293篇 |
2016年 | 508篇 |
2015年 | 535篇 |
2014年 | 762篇 |
2013年 | 1129篇 |
2012年 | 889篇 |
2011年 | 957篇 |
2010年 | 676篇 |
2009年 | 993篇 |
2008年 | 929篇 |
2007年 | 984篇 |
2006年 | 881篇 |
2005年 | 680篇 |
2004年 | 638篇 |
2003年 | 619篇 |
2002年 | 525篇 |
2001年 | 483篇 |
2000年 | 465篇 |
1999年 | 380篇 |
1998年 | 374篇 |
1997年 | 298篇 |
1996年 | 325篇 |
1995年 | 255篇 |
1994年 | 194篇 |
1993年 | 204篇 |
1992年 | 136篇 |
1991年 | 121篇 |
1990年 | 122篇 |
1989年 | 103篇 |
1988年 | 83篇 |
1987年 | 65篇 |
1986年 | 69篇 |
1985年 | 39篇 |
1984年 | 52篇 |
1983年 | 16篇 |
1982年 | 27篇 |
1981年 | 29篇 |
1980年 | 21篇 |
1979年 | 25篇 |
1978年 | 41篇 |
1977年 | 41篇 |
1976年 | 40篇 |
1975年 | 15篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Prof. Dr. Frank Glorius 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8047-8051
A general and efficient methodology for the direct transition metal free trifluoromethylthiolation of a broad range of biologically relevant N‐heteroarenes is reported employing abundant sodium chloride as the catalyst. This method is operationally simple, exhibits high functional group tolerance, and does not require protecting groups. 相似文献
12.
为判断动物试验方法是否具备实用性,分析了中国关于实用性的相关规定,通过4个典型案例对动物试验方法是否属于非治疗目的的外科手术方法、是否具备实用性进行了分析,总结判断标准并给出了撰写权利要求的建议。在撰写动物试验方法的专利申请时,应当注意该方法的目的及该方法是否包含外科手术步骤,并针对该方法的不同情况采用不同的撰写策略。 相似文献
13.
《中国物理 B》2021,30(5):56201-056201
A new three-dimensional(3 D) cellular model based on hinging open-cell Kelvin structure is proposed for its negative compressibility property. It is shown that this model has adjustable compressibility and does exhibit negative compressibility for some certain conformations. And further study shows that the images of compressibility are symmetrical about the certain lines, which indicates that the mechanical properties of the model in the three axial directions are interchangeable and the model itself has a certain geometric symmetry. A comparison of the Kelvin model with its anisotropic form with the dodecahedron model shows that the Kelvin model has stronger negative compressibility property in all three directions.Therefore, a new and potential method to improve negative compressibility property can be derived by selecting the system type with lower symmetry and increasing the number of geometric parameters. 相似文献
14.
电路特性的PSpice仿真方法比较 总被引:1,自引:0,他引:1
应用PSpice仿真软件的两种仿真方法,分析了串联型直流稳压电源的性能,比较了这两种仿真分析方法各自的优点.电路仿真实验表明,熟练掌握数种电路仿真方法是十分必要的,仿真方法对电路分析具有实际意义和作用. 相似文献
15.
家庭是人们生活居住的重要场所,伴人而居的害虫影响到人们的生活质量。因此,采用环境卫生防治、保管技术防治、化学防治、物理与机械防治、人工捕杀害虫等措施,能够有效地改善家庭生活环境。 相似文献
16.
叶红梅 《安徽工程科技学院学报:自然科学版》2003,18(3):77-79
为保证不同监测方法下监测数据的连续性、可比性以及正确判断环境空气变化规律,通过自动监测与传统的连续监测、五日法监测方法进行实验对比分析,找出传统方法与自动监测定值之间的偏差,探讨产生偏差的原因。 相似文献
17.
非线性互补问题的一种全局收敛的显式光滑Newton方法 总被引:2,自引:0,他引:2
本针对Po函数非线性互补问题,给出了一种显式光滑Newton方法,该方法将光滑参数μ进行显式迭代而不依赖于Newton方向的搜索过程,并在适当的假设条件下,证明了算法的全局收敛性。 相似文献
18.
M. Georgelin A. Pocheau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):169-174
The polycrystalline perovskitelike manganese oxides La1-xAxMnO (A = Na, and K, ) have been fabricated by sol-gel technique. For all the compositions explored in this work, the average manganese oxidation
state is practically constant, at for A = Na, and for A = K, respectively. A close relationship is confirmed to hold between the Curie temperature (Tc) and the bond distance of Mn-O. Results of magnetic measurements show that these materials can be utilized as suitable candidates
for magnetic refrigerants with wide applied temperature span, for their significant entropy change and the easily tuned Curie
temperature.
Received: 12 September 1997 / Revised: 18 December 1997 / Accepted: 21 January 1998 相似文献
19.
We discuss an error estimation procedure for the global error of collocation schemes applied to solve singular boundary value problems with a singularity of the first kind. This a posteriori estimate of the global error was proposed by Stetter in 1978 and is based on the idea of Defect Correction, originally due to Zadunaisky. Here, we present a new, carefully designed modification of this error estimate which not only results in less computational work but also appears to perform satisfactorily for singular problems. We give a full analytical justification for the asymptotical correctness of the error estimate when it is applied to a general nonlinear regular problem. For the singular case, we are presently only able to provide computational evidence for the full convergence order, the related analysis is still work in progress. This global estimate is the basis for a grid selection routine in which the grid is modified with the aim to equidistribute the global error. This procedure yields meshes suitable for an efficient numerical solution. Most importantly, we observe that the grid is refined in a way reflecting only the behavior of the solution and remains unaffected by the unsmooth direction field close to the singular point. 相似文献
20.
I.K. Argyros 《Applied Mathematics Letters》1997,10(6):21-28
In this note, we use inexact Newton-like methods to find solutions of nonlinear operator equations on Banach spaces with a convergence structure. Our technique involves the introduction of a generalized norm as an operator from a linear space into a partially ordered Banach space. In this way, the metric properties of the examined problem can be analyzed more precisely. Moreover, this approach allows us to derive from the same theorem, on the one hand, semilocal results of Kantorovich-type, and on the other hand, global results based on monotonicity considerations. By imposing very general Lipschitz-like conditions on the operators involved, on the one hand, we cover a wider range of problems, and on the other hand, by choosing our operators appropriately, we can find sharper error bounds on the distances involved than before. Furthermore, we show that special cases of our results reduce to the corresponding ones already in the literature. Finally, several examples are being provided where our results compare favorably with earlier ones. 相似文献