全文获取类型
收费全文 | 6929篇 |
免费 | 862篇 |
国内免费 | 567篇 |
专业分类
化学 | 4726篇 |
晶体学 | 110篇 |
力学 | 313篇 |
综合类 | 49篇 |
数学 | 859篇 |
物理学 | 2301篇 |
出版年
2023年 | 147篇 |
2022年 | 197篇 |
2021年 | 227篇 |
2020年 | 230篇 |
2019年 | 211篇 |
2018年 | 205篇 |
2017年 | 181篇 |
2016年 | 281篇 |
2015年 | 264篇 |
2014年 | 325篇 |
2013年 | 398篇 |
2012年 | 508篇 |
2011年 | 541篇 |
2010年 | 349篇 |
2009年 | 368篇 |
2008年 | 420篇 |
2007年 | 377篇 |
2006年 | 332篇 |
2005年 | 292篇 |
2004年 | 237篇 |
2003年 | 224篇 |
2002年 | 198篇 |
2001年 | 147篇 |
2000年 | 117篇 |
1999年 | 148篇 |
1998年 | 126篇 |
1997年 | 110篇 |
1996年 | 120篇 |
1995年 | 114篇 |
1994年 | 80篇 |
1993年 | 66篇 |
1992年 | 77篇 |
1991年 | 58篇 |
1990年 | 52篇 |
1989年 | 48篇 |
1988年 | 41篇 |
1987年 | 42篇 |
1986年 | 36篇 |
1985年 | 39篇 |
1984年 | 47篇 |
1983年 | 29篇 |
1982年 | 19篇 |
1980年 | 23篇 |
1979年 | 21篇 |
1978年 | 15篇 |
1976年 | 24篇 |
1975年 | 16篇 |
1974年 | 19篇 |
1973年 | 26篇 |
1972年 | 16篇 |
排序方式: 共有8358条查询结果,搜索用时 31 毫秒
61.
一种新的乙酰胆碱酶电极的研究 总被引:5,自引:0,他引:5
本文制备了一种以溶剂聚合膜PH电极作原电极,经高碘酸钠活化的醋酸纤维膜固定乙酰胆碱酯酶的乙酰胆碱生物电极。研究了酶固定化条件的影响,测得静态和动力学条件下的线性中响应范围分别为240-1300μg/mL和300-1700μg/mL将电极用于实际样品的回收率试验中,获得了满意的结果。 相似文献
62.
The principle of structure correlation is applied to 28 crystal structures which contain 44 different five-coordinate molybdenum fragments. The data derived map the reaction pathway for a bimolecular ligand substitution reaction at tetrahedral molybdenum centers. The dihedral-angle method from Muetterties and Guggenberger is employed in order to describe the interconversion between the trigonal bipyramidal (TBP) and the square pyramidal (SQP) conformations via the Berry pseudorotation mechanism in the system of Mo(L)_5 complexes. This structure correlation method provides a convincing mapping of the Berry pathway in this paper. 相似文献
63.
Shu-Lin Ma Zong-Hui Jiang Dai-Zheng Liao Shi-Ping Yan Geng-Lin Wang 《Transition Metal Chemistry》1994,19(5):531-533
Summary Two novel trinuclear complexes were prepared, namely [Cu2(oxae)2(H2O)2M] (ClO4)2, [oxae = N,N-bis(2-aminoethyl) oxamido dianion; M = Co and Ni]. Based on elemental analyses, conductivity measurements and i.r. spectra, the complexes are proposed to have extended oxamidobridged structures. The magnetic susceptibility of [Cu2-(oxae) 2(H2O)2Co](ClO4)2 were measured over the 4–300 K range and the observed data were successfully simulated by an equation based on the spin Hamiltonian, =–2J(1·2·2·3). The exchange integral, J, was found to be equal to –29.2 cm–1, indicating an antiferromagnetic spin-exchange interaction between the adjacent metal ions. 相似文献
64.
穿过液膜的自发电势振荡 总被引:2,自引:0,他引:2
An artificial membrane consisting of pricramic acid in nitrobenzene was used as an oil phase imposed between two aqueous phases. The right one contained trimethyl-slearylammonium chloride and aicohol; and the left contained sucrose solution (or H_2O). We found that this system exhibited rhythmic oscillation of electrical potential. The amplitude of the oscillations was between 20—150 mV. The oscillations were observed even when ethyl alcohol was absent in the aqueous of trimethylslearylammonium Chloride, and the increase in amplitude of oscillation with time was found to be less in the presence of sucrose. Some of the expremental results have been explained. 相似文献
65.
Kalyan Kali Sen Gupta Mrityunjoy Adbikary Subrata Kumar Mandal Shipra Sen Gupta 《Transition Metal Chemistry》1987,12(2):152-155
Summary The oxidation of MeCHO by chromium(VI) has been studied in HClO4 medium over a wide range of experimental conditions and has been found to obey the rate law;v=k[MeCHO][HCrO
4
–
][H+]. The calculated H
and-S
values for the reaction are 30±2kJ mol–1 and 171±7J mol–1deg–1, respectively. The mechanism is discussed in terms of carbon-hydrogen bond cleavage. 相似文献
66.
Xin Ying ZHANG Xue Sen FAN Hong Ying NIU Jian Ji WANGSchool of Chemical Environmental Sciences Henan Normal University Key Laboratory ofEnvironmental Science Engineering of Henan Education Department Xinxiang 《中国化学快报》2003,(10)
a, a'-Bis(substituted benzylidene)cycloalkanones were efficiently prepared from cycloalkanones and benzaldehydes in [bmim][BF4] by using iron(III) chloride hexahydrate as a catalyst. It is shown that [bmim][BF4] and iron(III) chloride hexahydrate can be quantitatively recovered and be reused effectively for many times. Compared with the known methods, this novel process has the advantage of being an envkonmentally benign process together with good yields and mild reaction conditions. 相似文献
67.
68.
69.
70.
The perfluorohexylated 3,4-ethylenedioxythiophene 5 was prepared via Mitsunobu reaction of perfluorohexylatyed diol 2 with diethyl 3,4-dihydroxythiophenedicarboxylate followed by decarboxylation. The polymerization of 5 was conducted with both oxidative chemical and electrochemical polymerizations. The polymers were characterized by cyclic voltammogram, UV, IR, TGA and DSC. 相似文献