全文获取类型
收费全文 | 6278篇 |
免费 | 738篇 |
国内免费 | 715篇 |
专业分类
化学 | 5033篇 |
晶体学 | 74篇 |
力学 | 254篇 |
综合类 | 59篇 |
数学 | 776篇 |
物理学 | 1535篇 |
出版年
2024年 | 8篇 |
2023年 | 77篇 |
2022年 | 159篇 |
2021年 | 168篇 |
2020年 | 204篇 |
2019年 | 230篇 |
2018年 | 176篇 |
2017年 | 147篇 |
2016年 | 269篇 |
2015年 | 226篇 |
2014年 | 311篇 |
2013年 | 426篇 |
2012年 | 475篇 |
2011年 | 458篇 |
2010年 | 318篇 |
2009年 | 315篇 |
2008年 | 360篇 |
2007年 | 330篇 |
2006年 | 311篇 |
2005年 | 284篇 |
2004年 | 279篇 |
2003年 | 280篇 |
2002年 | 331篇 |
2001年 | 271篇 |
2000年 | 196篇 |
1999年 | 202篇 |
1998年 | 102篇 |
1997年 | 84篇 |
1996年 | 112篇 |
1995年 | 95篇 |
1994年 | 57篇 |
1993年 | 57篇 |
1992年 | 50篇 |
1991年 | 44篇 |
1990年 | 46篇 |
1989年 | 28篇 |
1988年 | 31篇 |
1987年 | 26篇 |
1986年 | 20篇 |
1985年 | 32篇 |
1984年 | 13篇 |
1983年 | 15篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1974年 | 8篇 |
排序方式: 共有7731条查询结果,搜索用时 2 毫秒
171.
Sílvia S. P. R. Almeida Joo J. R. Fraústo Da Silva Armando J. L. Pombeiro 《Journal of organometallic chemistry》1993,450(1-2)
Treatment of a THF solution of trans-[ReCl(N2)(dppe)2] (dppe = Ph2PCH2CH2PPh2) with a 1-alkyne HCCR (R =tBu, CO2Me, CO2Et, or C6H4Me-4), in the presence of Tl[BF4]/[NH4][BF4], under sunlight, affords the corresponding carbyne-fluoro complexes trans-[ReF(CCH2R)(dppe)2][BF4] in an unprecedented single-pot synthesis. Further reaction with [BU4N]OH leads to the vinylidenefluoro compounds trans-[ReF(=C=CHR)(dppe)2] (R = CO2Me, CO2Et, or C6H4Me-4). 相似文献
172.
173.
Da Yeon Park 《Tetrahedron letters》2006,47(37):6641-6645
Polysubstituted benzene derivatives were synthesized starting from the Baylis-Hillman adducts via the sequential introduction of primary nitroalkane at the primary position, Michael addition to β-branched Michael acceptor, aldol condensation, elimination of nitrous acid, and the final aromatization process. 相似文献
174.
In a previous paper, a scheme of integral approximation was proposed, in which a large number of two-electron integrals containing a certain kind of orbital pairs, i.e., weakly related pairs, can be neglected. A new criterion for partitioning orbital pairs into two groups, i.e., strongly and weakly related pairs, is introduced in order to allow for neglect of more integrals without sacrificing the accuracy of a computation. Test calculations on the BH3? C2H4 complex show that by the use of the new version, results of roughly the same accuracy as was obtained by the old version is obtained by retaining 80% of the integrals used in the old version. This kind of saving is more significant for larger molecules. For example, in a calculation on Cu-porphine with 203 CGTO 'S , the revised version will require about 2.0 × 106 integrals, while the original version will require about 4.5 × 106. And these two approximate calculations are expected to give the results of roughly the same accuracy. 相似文献
175.
You WK So SH Lee H Park SY Yoon MR Chang SI Kim HK Joe YA Hong YK Chung SI 《Experimental & molecular medicine》1999,31(4):197-202
Endostatin, a carboxyl-terminal fragment of collagen XVIII is known as an anti-angiogenic agent, that specifically inhibits the proliferation of endothelial cell and the growth of several primary tumor. We report here the purification and characterization of the recombinant murine endostatin (rmEndostatin) which was expressed in a prokaryotic expression system. This rmEndostatin has similar physiochemical properties of yeast-produced recombinant endostatin, and it also specifically inhibits the proliferation and migration of bovine capillary endothelial cells stimulated by basic fibroblast growth factor. The biological activity of rmEndostatin was also shown by its anti-angiogenic ability on the chorioallantoic membrane of chick embryo in vivo. In this article, we demonstrate the refolding and purification of rmEndostatin, expressed using E. coli system, to a biologically active and soluble form. In addition, these results confirm the activity of endostatin as a potent anti-angiogenic agent. 相似文献
176.
Seghezzo L Trupiano AP Liberal V Todd PG Figueroa ME Gutiérrez MA Da Silva Wilches AC Iribarnegaray M Guerra RG Arena A Cuevas CM Zeeman G Lettinga G 《Applied biochemistry and biotechnology》2003,109(1-3):167-180
A pilot-scale sewage treatment system consisting of two upflow anaerobic sludge bed (UASB) reactors followed by five waste stabilization ponds (WSPs) in series was studied under subtropical conditions. The first UASB reactor started up in only 1 mo (stable operation, high chemical oxygen demand [COD] removal efficiency, low volatile fatty acids concentration in the effluent, alkalinity ratio above 0.7, biogas production above 0.1 Nm3/kg of CODremoved). Removal efficiencies up to 90% were obtained in the anaerobic steps at a hydraulic retention time of 6 + 4 h (80% removal in the first step). Fecal coliform removal in the whole system was 99.9999% (99.94% in anaerobic steps and 99.98% in WSPs). COD balances over UASB reactors are provided. A minimum set of data necessary to build COD balances is proposed. Intermittent sludge washout was detected in the reactors with the COD balances. Sludge washout from single-step UASB reactors should be monitored and minimized in order to ensure constant compliance with discharge standards, especially when no posttreatment is provided. The system combined high COD and fecal coliform removal efficiency with an extremely low effluent concentration, complying with discharge standards, and making it an attractive option for sewage treatment in subtropical regions. 相似文献
177.
Determination of Partial Molar Volumes of EPA and DHA Ethyl Esters in Supercritical Carbon Dioxide 总被引:4,自引:0,他引:4
Mei HUANG Xian Da WANG Ren Tian XIONG Ping Dong WU Qi Long REN* National Laboratory of Secondary Resources Chemical Engineering Zhejiang University Hangzhou 《中国化学快报》2002,13(1)
The use of supercritical fluids (SCFs) as solvents has been attracting widespread interest in the research and commercial applications. The study of partial molar volumes of solutes at infinite dilution in the near-critical region is of considerable fundamental importance, as these data reflects the interactions occurring between the solute and the solvent. Experimental measurements of partial molar volumes may be divided into two categories: direct and indirect methods. The direct methods… 相似文献
178.
Monoclonal antibody technique was employed to detect the conformational difference of CaM induced by metal ions. A trivalent europium ion induced conformation-specific anti-calmodulin monoclonal antibody was successfully prepared with europium-saturated calmodulin as antigen. 相似文献
179.
180.