全文获取类型
收费全文 | 100652篇 |
免费 | 19890篇 |
国内免费 | 35649篇 |
专业分类
化学 | 72674篇 |
晶体学 | 4165篇 |
力学 | 8023篇 |
综合类 | 3849篇 |
数学 | 17012篇 |
物理学 | 50468篇 |
出版年
2024年 | 261篇 |
2023年 | 1082篇 |
2022年 | 3588篇 |
2021年 | 3599篇 |
2020年 | 3541篇 |
2019年 | 3422篇 |
2018年 | 3194篇 |
2017年 | 4780篇 |
2016年 | 3550篇 |
2015年 | 5110篇 |
2014年 | 6236篇 |
2013年 | 8199篇 |
2012年 | 8167篇 |
2011年 | 8811篇 |
2010年 | 8859篇 |
2009年 | 9177篇 |
2008年 | 10190篇 |
2007年 | 9170篇 |
2006年 | 8939篇 |
2005年 | 7762篇 |
2004年 | 6061篇 |
2003年 | 4295篇 |
2002年 | 4296篇 |
2001年 | 4413篇 |
2000年 | 4648篇 |
1999年 | 2628篇 |
1998年 | 1452篇 |
1997年 | 1139篇 |
1996年 | 1031篇 |
1995年 | 974篇 |
1994年 | 997篇 |
1993年 | 973篇 |
1992年 | 845篇 |
1991年 | 611篇 |
1990年 | 613篇 |
1989年 | 629篇 |
1988年 | 488篇 |
1987年 | 413篇 |
1986年 | 314篇 |
1985年 | 255篇 |
1984年 | 263篇 |
1983年 | 233篇 |
1982年 | 195篇 |
1981年 | 199篇 |
1980年 | 134篇 |
1979年 | 142篇 |
1978年 | 51篇 |
1977年 | 33篇 |
1965年 | 33篇 |
1959年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
TaoJIANG BuXingHAN GuoYingZHAO ZhongHaoLI YanHongCHANG HaiXiangGAO JunChunLI 《中国化学快报》2004,15(3):296-299
The oxidation of styrene with molecular oxygen catalyzed by PdCl2 CuCl2 has been investigated in supercritical CO2 with a batch reactor. The oxidative system of styrene contains four components at the beginning and seven components during the reaction. The critical temperature, critical pressure, and critical density at different conversions are determined by using a high-pressure view cell. The effect of phase behavior on the conversion and selectivity were studied. Experimental results showed that the critical parameters of the reaction mixture at fixed initial molar ratio changed with the conversion of reactant. The conversion of styrene reached maximum near the critical density of the reaction mixture. Product selectivity also varied with density of reaction mixture and could be tuned to some degree. 相似文献
992.
XinYingZHANG XueSenFAN JianJiWANG YanZhenLI 《中国化学快报》2004,15(10):1170-1172
Quinoline derivatives were efficiently prepared through acid-catalyzed Friedlander reaction in ionic liquid ([bmim] [BF4]). It is shown that the proposed method is operationally simple and environmentally benign in that the reaction media and the catalyst can be recovered and be reused effectively for at least four times. 相似文献
993.
A new polyoxomolybdate complex HNa7[Mo36O112(H2O)16]·47H2O 1 has been prepared in the beaker solution and characterized by single-crystal X-ray diffraction and elemental analyses. Crystal data: H127Mo36Na7O175, Mr = 6542.79, monoclinic, C2/c, a = 40.891(6), b = 17.900(3), c = 25.580(4) , β = 125.673(2)°, V = 15210(4) 3, Z = 4, Dc = 2.857 g/cm3, F(000) = 12464, μ = 3.013 mm-1, R = 0.0633 and wR = 0.1654 (I > 2σ(I)). With the bridging sodium cations, the [Mo36O112(H2O)16]8- units in compound 1 are linked to form a one-dimensional structure, on the basis of which a three-dimensional architecture is further constructed via other sodium cations and complicated hydrogen bonds. 相似文献
994.
LIU Tie-mei WANG Shu-sheng ZHU Guang-ze LI Ming-yang ZHANG Li-ping 《高等学校化学研究》2007,23(3):300-302
Antibody-directed enzyme prodrug therapy(ADEPT) is a new strategy for the treatment of cancer that has arisen in recent twenty years, the main merits of which are that it can improve the selectivity of anticancer drugs and reduce the side effects in remote tissue. In the present study, two prodrugs-glycosylated aromatic nitrogen mustard derivatives were synthesized. Glucose and lactose were converted into glycosyl donors-trichloroacetimidate; the obtained glycosyl donors were glycosylated with p-nitrophenol(glycosyl donors) to form β-glucosyl p-nitrobenzene and β-lactosyl p-nitrobenzene that were protected by acetyl in a stereoselective manner; the two products were reduced by zinc dust and then treated with ethylene oxide, afforded two glycosylated nitrogen mustard derivatives that were protected by acetyl; the last step was to deacetylate and then afforded the two target compounds that could be used as prodrugs of ADEPT for further Anti-tumor research. 相似文献
995.
996.
为寻找新的高活性农药 ,根据生物等排原理 ,设计合成了 10种未见文献报道的N′ 5 ( 1H 1,2 ,3 ,4 四唑基 ) N 芳甲酰基硫脲类化合物 .它们的结构经IR ,1HNMR和元素分析确证 .初步的生物活性测定结果表明 ,部分化合物具有优良的除草活性或植物生长调节活性 . 相似文献
997.
合成了两种新的聚醚取代的水杨醛亚胺Schiff碱锰(III)配合物MnL12Cl和MnL2Cl,研究了它们与表面活性剂2Brij35形成的金属胶束对BNPP的催化水解反应.探讨了催化反应机理,提出了水解反应的动力学数学模型;计算了催化反应的Michanelis常数和表观活化能,并与不含聚醚链的类似物MnL2Cl比较,考查了配合物配体中聚醚支链及其3端基对催化水解反应的影响.结果表明,催化水解反应遵循金属-氢氧离子机理;以羟基作为聚醚链端基的MnL12Cl的催化活性最高,在相同条件下,其表观一级速率常数约为MnL2Cl的3倍,为MnL2Cl的30倍.23 相似文献
998.
Qing LI Hui LI Bin SU Xiang Bao MENG Meng Shen CAI Zhong Jun LI* Department of Chemical Biology School of Pharmaceutical Sciences National Research Laboratory of Natural Biomimetic Drugs Peking University Beijing 《中国化学快报》2002,13(4):303-305
Our previous paper1,2reported the results of selective synthesis of mannose type glycosides and their dimers in our attempt to synthesize derivatives of N-acetyllacto- samine, which could have potential activity of anti-metastasis3. Further studies on the glycosylation of the accepters exploiting glycosyl nitrate instead of the acetate as donor showed interesting chemoselectivity between the two kinds of donor, namely, the glucose type and the mannose type. The reactivity difference of the t… 相似文献
999.
烷氧桥相连的四苯基双金属卟啉配合物的红外光谱研究 总被引:1,自引:1,他引:1
研究了烷氧桥相连的四苯基双卟啉及其Mn(Ⅱ),Fe(Ⅲ),Co(Ⅱ)配合物的红外光谱(3600~150cm^-1),对一些主要吸收谱带进行了经验归属,金属敏感谱带出现1558.2(以H2P-H2P为例)、1477.2,1401.9,1350.5,1001.7,965.9,877.3和798.8cm^-1附近,金属和烷氧桥都敏感的谱带出现在1595.1(以H2P为例)、1491.1,851.1和72 相似文献
1000.