全文获取类型
收费全文 | 111320篇 |
免费 | 8345篇 |
国内免费 | 10172篇 |
专业分类
化学 | 47245篇 |
晶体学 | 800篇 |
力学 | 9633篇 |
综合类 | 1665篇 |
数学 | 33414篇 |
物理学 | 37080篇 |
出版年
2024年 | 169篇 |
2023年 | 994篇 |
2022年 | 2176篇 |
2021年 | 2291篇 |
2020年 | 2423篇 |
2019年 | 2630篇 |
2018年 | 2228篇 |
2017年 | 2646篇 |
2016年 | 2990篇 |
2015年 | 2617篇 |
2014年 | 3874篇 |
2013年 | 7305篇 |
2012年 | 4570篇 |
2011年 | 5044篇 |
2010年 | 4258篇 |
2009年 | 6127篇 |
2008年 | 6746篇 |
2007年 | 7291篇 |
2006年 | 6575篇 |
2005年 | 5565篇 |
2004年 | 4982篇 |
2003年 | 5158篇 |
2002年 | 5197篇 |
2001年 | 4077篇 |
2000年 | 3951篇 |
1999年 | 3451篇 |
1998年 | 3271篇 |
1997年 | 2491篇 |
1996年 | 2239篇 |
1995年 | 1977篇 |
1994年 | 1903篇 |
1993年 | 1527篇 |
1992年 | 1541篇 |
1991年 | 1151篇 |
1990年 | 1004篇 |
1989年 | 844篇 |
1988年 | 757篇 |
1987年 | 638篇 |
1986年 | 557篇 |
1985年 | 594篇 |
1984年 | 587篇 |
1983年 | 311篇 |
1982年 | 468篇 |
1981年 | 518篇 |
1980年 | 377篇 |
1979年 | 380篇 |
1978年 | 307篇 |
1977年 | 290篇 |
1976年 | 212篇 |
1973年 | 152篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
M.A. Tawhid 《Journal of Optimization Theory and Applications》2002,113(1):149-164
In this paper, we give some sufficient conditions for the local uniqueness of solutions to nonsmooth variational inequalities where the underlying functions are H-differentiable and the underlying set is a closed convex set/polyhedral set/box/polyhedral cone. We show how the solution of a linearized variational inequality is related to the solution of the variational inequality. These results extend/unify various similar results proved for C
1 and locally Lipschitzian variational inequality problems. When specialized to the nonlinear complementarity problem, our results extend/unify those of C
2 and C
1 nonlinear complementarity problems. 相似文献
62.
双掺(Tm3+,Tb3+)LiYF4激光器1.5 μm波长激光阈值分析 总被引:1,自引:0,他引:1
由速率方程推出了双掺(Tm^3 ,Tb^3 )离子准四能级系统的激光阈值解析式,讨论了Tm^3 和Tb^3 离子之间的相互作用。分析了1.5μm波长附近的激光阈值和Tm^3 、Tb^3 离子的掺杂原子数分数及晶体长度的关系。结果表明,对于对应Tm^3 离子^3H4→^3F4跃迁的约1.5μm波长的激光,激活离子Tm^3 的掺杂原子数分数过大时,交叉弛豫作用将使系统阈值迅速增加。Tb^3 离子的加入,一方面能抽空激光下能级,起到降低阈值的作用;另一方面亦减少了激光上能级的寿命,使阈值升高。故Tb^3 离子有最佳掺杂原子数分数。对于Tm原子数分数为y=0.01的Tm:LiYF4晶体,Tb^3 离子的最佳掺杂原子数分数为0.002左右,同时表明,激光阈值与晶体长度有关。最佳晶体长度与Tm^3 、Tb^3 离子的掺杂原子数分数以及晶体的衍射损耗和吸收损耗有关。 相似文献
63.
Pulse radiolysis with kinetic spectroscopic detection was applied to study the kinetics of the first steps of radiation induced polymerization of cyclohexyl acrylate and cyclohexyl methacrylate in cyclohexane solvent. The reactions were initiated by cyclohexyl radicals produced in the radiolysis of the solvent. The transient absorption spectra of the -carboxyalkyl type radicals produced in addition reaction show maxima around 300 nm. This shifts to longer wavelength with time after the pulse. This phenomenon was explained by the oligomerization reaction. From the kinetic curves average rate coefficients of termination for the oligomer radicals (2kt) were determined as a function of time elapsed after the electron pulse. The values obtained were compared with those calculated for other (acrylate and methacrylate type) monomers. 相似文献
65.
It is proved that for any integerk≥ 54 000, there isN
k
>0 depending onk only such that every even integer ≥N
k
is a sum of two odd prime numbers andk powers of 2.
Project partially supported by RGC Research Grant (No.HKU 7122/97P) and Post-Doctoral Fellowship of the University of Hong
Kong. 相似文献
66.
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
67.
68.
在氢化丁苯共聚物13C-NMR谱脂肪碳部分谱带归属的基础上,根据各谱带的主要来源,推导出六个二单元浓度的计算公式。计算出二单元、一单元的相对含量,各结构单元的数均序列长度、嵌段含量和其它结构参数。加氢前后的1H-和13C-NMR谱的组成计算结果基本一致。初步探讨了作为粘度指数改进剂的氢化丁苯共聚物微观结构与性能的关系,为合成提供了依据。 相似文献
69.
超临界流体色谱流程设计及其应用 总被引:1,自引:1,他引:0
本文设计了多功能超临界流体色谱流程,流程中包括毛细管/微填充柱SFC,GC,计算机控制温度、压力、密度及信号采集、处理,配置有超临界流体萃取池,解决了超临界流体色谱分流口易堵问题。利用该流程,将石腊、DC-200气相色谱固定相、黄油、蜂蜡、救心油、红花油等样品进行超临界流体色谱分离。 相似文献
70.
Transparent conducting ZnO:AI thin films with good adhesion and Iow resistivity have been prepared on organic substrates and Coming 7059 glass substrates by r.f. magnetron-sputtering technique at Iow substrate temperature (25-210℃). Structural and photoelectric properties of the deposited films are investigated. The deposited films are polycrystalline with hexagonal structure and a preferred orientation with the c-axis perpendicular to the substrate. Only the (002) peak is observed.High quality films with resistivity as Iow as 1.0 x 10- 3Ω@ cm and 8.4 x 10- 4Ω@ cm, the average transmittance over 74% and 85% in the wavelength range of the visible spectrum have been obtained on different substrates. 相似文献