全文获取类型
收费全文 | 85424篇 |
免费 | 14742篇 |
国内免费 | 9991篇 |
专业分类
化学 | 61142篇 |
晶体学 | 916篇 |
力学 | 5247篇 |
综合类 | 507篇 |
数学 | 9627篇 |
物理学 | 32718篇 |
出版年
2024年 | 202篇 |
2023年 | 1748篇 |
2022年 | 2714篇 |
2021年 | 3102篇 |
2020年 | 3582篇 |
2019年 | 3385篇 |
2018年 | 2953篇 |
2017年 | 2828篇 |
2016年 | 4147篇 |
2015年 | 4061篇 |
2014年 | 4859篇 |
2013年 | 6318篇 |
2012年 | 7977篇 |
2011年 | 8186篇 |
2010年 | 5559篇 |
2009年 | 5244篇 |
2008年 | 5671篇 |
2007年 | 5103篇 |
2006年 | 4680篇 |
2005年 | 3803篇 |
2004年 | 2912篇 |
2003年 | 2306篇 |
2002年 | 2190篇 |
2001年 | 1867篇 |
2000年 | 1625篇 |
1999年 | 1788篇 |
1998年 | 1443篇 |
1997年 | 1408篇 |
1996年 | 1375篇 |
1995年 | 1135篇 |
1994年 | 988篇 |
1993年 | 838篇 |
1992年 | 724篇 |
1991年 | 618篇 |
1990年 | 524篇 |
1989年 | 419篇 |
1988年 | 353篇 |
1987年 | 293篇 |
1986年 | 267篇 |
1985年 | 216篇 |
1984年 | 148篇 |
1983年 | 106篇 |
1982年 | 83篇 |
1981年 | 70篇 |
1980年 | 67篇 |
1979年 | 32篇 |
1978年 | 30篇 |
1977年 | 40篇 |
1976年 | 31篇 |
1973年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
The paper advanced the theoretical procedures for quantitative design on selective stacking of zwitterions in full capillary sample matrix by a cathodic-direction moving reaction boundary (MRB) in capillary electrophoresis (CE) under control of electroosmotic flow (EOF). With the procedures, we conducted the theoretical computations on the selective stacking of two test analytes of L-histidine (His) and L-tryptophan (Trp) by the MRB created with 30 mM pH 3.0 formic acid-NaOH buffer and 2-80 mM sodium formate. The results revealed the following three predictions. At first, the MRB cannot stack His and Trp plugs if less than 12.5 mM sodium formate is used to form the MRB and prepare the sample matrix. Second, the MRB can stack His and/or Trp sample plugs completely if higher than 50 mM sodium formate is chosen to form the MRB. Third, the MRB can only focus His plug completely, but stack Trp plug partially if 20-50 mM sodium formate is used; this implied the complete MRB-induced selective stacking to His rather than Trp. All the three predictions were quantitatively proved by the experiments. With great dilution of sample matrix and control of EOF, controllable, simultaneous and MRB-induced selective stacking and separation of zwitterions were achieved. The theoretical results hold evident significances to the quantitative design of selective stacking conditions and the increase of detection sensitivity of zwitterions in CE. In addition, the control of EOF by cetyltrimethylammonium bromide (CTAB) can evidently improve the stacking efficiency to both His and Trp. 相似文献
882.
碳铂类似物的合成,表征及对大鼠W—256肉瘤的抑制作用 总被引:2,自引:0,他引:2
合成了十八种〔PtA_2X〕·yH_2O,其中A分别为NH_3、CH_3NH_2、1/2乙二胺和1/2(2,3-二甲基-2,3-丁二胺),X分别为1,1-环丙烷二羧酸根(CPrDCA)、2-甲-1,1-环丙烷二羧酸根(2-M-CPrDCA)、2-甲-1,1-环丁烷二羧酸根(2-M-CBDCA)、1,2-环戊烷二羧酸根(CPDCA)和1,1-环已烷二羧酸根(CHDCA),并进行了表征。测定了配合物抑制大鼠W-256肉瘤的活性,发现配合物〔Pt(NH_3)_2X〕系列按X不同有以下的活性次序:CPrDCA>2-M-CPrDCA>CPDCA>CBDCA(碳铂)≥2-M-CBDCA。 相似文献
883.
884.
For the equilibrium immiscible Co-Ag system, a proven realistic ab initio derived n-body potential is applied to study the nonequilibrium solid phase formation at three chemical stoichiometries of Co/Ag = 1:3, 1:1, and 3:1. To predict the structural stability, the elastic constants and the phonon spectra are calculated at the chosen stoichiometries with a total of eight hypothetical crystalline structures. The calculated results suggest that four compounds, that is, D0(3) CoAg3, B1 CoAg, B2 CoAg, and D0(3) Co3Ag, are unstable, as they all feature negative elastic constants as well as imaginary phonons, and that another four compounds of both fcc-type L1(2) and hcp-type D0(19) structures at chemical stoichiometries of Co/Ag = 1:3 and 3:1, respectively, may elastically be favored and therefore obtainable under some specific conditions. It is also found that all the calculated elastic constants and phonon spectra are coincident within the framework of the elastic theory. Moreover, the calculated elastic constants are in good agreement with those acquired directly from ab initio calculations, lending support to the validity of the ab initio derived n-body Co-Ag potential as well as its resultant elastic constants and the phonon spectra. Interestingly, some of the predicted nonequilibrium solid phases, that is, two hcp-type compounds at chemical stoichiometries of Co/Ag = 1:3 and 3:1, respectively, are indeed obtained in ion beam mixing experiments and their lattice constants determined by diffraction analysis are in good agreement with those from calculations. 相似文献
885.
X. H. Liu M. Sun J. J. Yue Y. X. Yin X. L. Liu F. M. Miao 《Journal of Molecular Structure》2003,620(2-3):227-230
In this paper, we carried out a theoretical study on the active site structures of the Mn-SOD with ab initio Hartree–Fock SCF method, and analyzed the molecular orbital energies, charges and atomic orbital contribution to the frontier molecular orbital. 相似文献
886.
Chao Wang Jing Wang Xiang Xiao Guobin Zhong Shijia Wu Kaiqi Xu Wei Zhao Wei Su Jie Zeng Baojun Wu Weili Zhang Changcheng Wu Zhiqiang Shi 《中国化学快报》2019,30(6):1269-1272
A novel cyclic ammonium salt, N,N-dimethylpyrrolidinium tetrafluoroborate (P11-BF4), was successfully synthesized for the first time. The smallest cyclic structure of P11-BF4 induced high solubility and conductivity in PC, which can easier enter the micropores of activated carbon and occupy more surface area during charge/discharge process. 相似文献
887.
888.
本工作用四种较新的质谱技术(碰撞诱导解离(CID),电荷剥离(CS),电荷分离(CSe),电子捕获诱导解离(ECID)谱研究了邻、间、对溴甲苯和溴化苄四种异构体。四种技术在一定程度上都可区分这些异构体。其中比较四种异构体ECID谱中ECID峰的相对强度可得到满意的区分效果。 相似文献
889.
890.