全文获取类型
收费全文 | 50620篇 |
免费 | 9050篇 |
国内免费 | 7520篇 |
专业分类
化学 | 37091篇 |
晶体学 | 786篇 |
力学 | 3140篇 |
综合类 | 525篇 |
数学 | 5576篇 |
物理学 | 20072篇 |
出版年
2024年 | 161篇 |
2023年 | 938篇 |
2022年 | 1811篇 |
2021年 | 1907篇 |
2020年 | 2000篇 |
2019年 | 2104篇 |
2018年 | 1793篇 |
2017年 | 1827篇 |
2016年 | 2429篇 |
2015年 | 2618篇 |
2014年 | 3227篇 |
2013年 | 4102篇 |
2012年 | 4784篇 |
2011年 | 4942篇 |
2010年 | 3584篇 |
2009年 | 3605篇 |
2008年 | 3831篇 |
2007年 | 3323篇 |
2006年 | 2978篇 |
2005年 | 2444篇 |
2004年 | 1891篇 |
2003年 | 1544篇 |
2002年 | 1535篇 |
2001年 | 1255篇 |
2000年 | 1061篇 |
1999年 | 850篇 |
1998年 | 647篇 |
1997年 | 556篇 |
1996年 | 527篇 |
1995年 | 426篇 |
1994年 | 440篇 |
1993年 | 342篇 |
1992年 | 290篇 |
1991年 | 236篇 |
1990年 | 225篇 |
1989年 | 165篇 |
1988年 | 123篇 |
1987年 | 102篇 |
1986年 | 110篇 |
1985年 | 87篇 |
1984年 | 53篇 |
1983年 | 44篇 |
1982年 | 19篇 |
1981年 | 24篇 |
1980年 | 15篇 |
1979年 | 30篇 |
1977年 | 17篇 |
1976年 | 13篇 |
1975年 | 12篇 |
1957年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Jiang Wei 《Journal of Mathematical Analysis and Applications》2004,297(1):305-316
The eigenvalue and the stability of singular differential systems with delay are considered. Firstly we investigate some properties of the eigenvalue, then give the exact exponential estimation for the fundamental solution, and finally discuss the necessary and sufficient condition of uniform asymptotic stability. 相似文献
42.
Leong‐Huat Gan Palaniswamy Ravi Bao Wei Mao Kam‐Chiu Tam 《Journal of polymer science. Part A, Polymer chemistry》2003,41(17):2688-2695
Polymerization of 2‐(diethylamino)ethyl methacrylate (DEAEMA) via homogeneous atom transfer radical polymerization under various reaction conditions is described. The effects of the initiators and solvents were examined. With 1,1,4,7,10,10‐hexamethyl triethylenetetramine/copper(I) chloride/p‐toluenesulfonyl chloride as the ligand/catalyst/initiator system in methanol, poly(DEAEMA) with a polydispersity index as low as 1.07 was synthesized. Kinetic studies demonstrated the polymerization was very well controlled and exhibited the living characteristic of the process. Well‐defined block copolymers of DEAEMA and tert‐butyl methacrylate (tBMA) were successfully synthesized. The copolymers could be synthesized with equally good results by starting with either p(DEAEMA) or p(tBMA) as the macroinitiators. However, only the macroinitiators terminated with chlorine should be used. The corresponding macroinitiators with bromine as a transferable group did not yield well‐defined copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2688–2695, 2003 相似文献
43.
This paper has demonstrated that the Schwartz alternating process must converge if D-N alternating process has converged. Its technique is that the overlapping regions in Schwartz alternating process are considered as independent domains, then Schwartz alternating process could be transformed into D-N alter-nating process. Finally the convergence estimation of Schwartz alternating process could be obtained. The results show that its convergence rate is same as that of D-N alternating process. 相似文献
44.
45.
考虑到量子相干效应和界面散射效应 ,利用 L ambert理论模型 ,计算正常金属 /绝缘层 /超导 /绝缘层 /正常金属双垒隧道结中的准粒子输运系数和隧道谱。研究表明 :( 1)所有的准粒子输运系数和电导谱在超导能隙之上都随能量作周期性振荡 ,其振荡周期依赖于超导层的厚度 ;( 2 )在超导能隙之上 Andreev反射系数随能量呈现周期性消失现象 ;( 3)在绝缘层势垒强度取很大的隧道极限下 ,超导层中会形成一系列的准粒子束缚态 ,其位置由量子化条件决定 ;( 4)界面散射效应不仅能压低各子能隙电导峰 ,还能使子能隙电导峰劈裂为两个峰。 相似文献
46.
47.
A new method based on anion exchange resin separation and graphite furnace atomic absorption spectrometry (GFAAS) detection
is proposed for the determination of inorganic tin species. The result showed that Sn(IV) was quantitatively retained on the
resin when [HCl] = 9.0 mol · L−1, but Sn(II) could not be adsorbed on the resin under the same condition. Thus, a separation of Sn(II) and Sn(IV) has been
realized. When the concentration of NaOH solution was between 2.0–7.0 mol · L−1, Sn(IV) that adsorbed on the resin could be eluated from the resin completely. Meanwhile, under the atmosphere and the nitrogen
states, the translation between Sn(II) and Sn(IV) was investigated. Under the optimal conditions, the detection limit of Sn(IV)
is 0.40 μg · L−1 with RSD of 2.3% (n = 5, c = 2.0 μg · L−1). The proposed method was applied to the speciation analysis of tin in different water samples and the recovery of total
Sn was in the range of 98.7–101.7%. In order to verify the accuracy of the method, a certified reference water sample was
analyzed and the results obtained were in good agreement with the certified value. 相似文献
48.
The properties of pulsed laser vapor doping on p-Si(1 0 0) with a KrF (248 nm) excimer pulsed laser (248 nm) and BCl3 gas are reported in this paper. The doped samples are characterized by the resistance measured using a four-probe method, since the sheet resistance changes with the carrier concentration of the sample. The doping effects with the variation of laser energy density, pulse number, and the pressure of BCl3 were investigated in terms of the sheet resistance. In this way, the optimized parameters were obtained and used for the positive heavy doping on p-Si(1 0 0) and p-Si(1 1 1). Then, using a square mesh under the above conditions, an image doping was completed. Finally, the metal–semiconductor Ohmic contacts were realized by plating Ag and Cu films on the doped surface. 相似文献
49.
Characteristics and structures of weak efficient surfaces of production possibility sets 总被引:1,自引:0,他引:1
Quanling Wei Hong Yan Gang Hao 《Journal of Mathematical Analysis and Applications》2007,327(2):1055-1074
This paper studies the characteristics and structure of the weak surface of the production possibility set. We apply techniques and methods of transferring a polyhedral cone from its intersection form to its sum form, identify an intersection representation of the production possibility set. We give the structure theorem of weak surface of the production possibility set, which includes three complementary slackness conditions. We define the input weak efficiency and output weak efficiency for different DEA models according to the representation of the intersection form. It investigates the characteristics of the weak surfaces, and proves the structure theorems of input weak DEA efficiency and output weak DEA efficiency. The structure theorems establish weighted combination of inputs and outputs that are weak DEA efficient. Numerical examples are provided for illustration. 相似文献
50.
Zhen‐Feng Chen Hong‐Li Zhou Hong Liang Yan Li Ren‐Gen Xiong Xiao‐Zeng You 《应用有机金属化学》2003,17(11):883-884
The centrosymmetric binuclear structure of [Pb2(H‐Norf)2(ONO2)4]shows the geometry around each lead(II) atom to be distorted trigonal bipyramidal with Pb–O distances ranging from 2.357(3) to 2.769(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献