全文获取类型
收费全文 | 7748篇 |
免费 | 1274篇 |
国内免费 | 1904篇 |
专业分类
化学 | 6371篇 |
晶体学 | 217篇 |
力学 | 433篇 |
综合类 | 140篇 |
数学 | 1108篇 |
物理学 | 2657篇 |
出版年
2024年 | 10篇 |
2023年 | 50篇 |
2022年 | 218篇 |
2021年 | 217篇 |
2020年 | 230篇 |
2019年 | 274篇 |
2018年 | 234篇 |
2017年 | 266篇 |
2016年 | 295篇 |
2015年 | 401篇 |
2014年 | 427篇 |
2013年 | 594篇 |
2012年 | 605篇 |
2011年 | 636篇 |
2010年 | 582篇 |
2009年 | 619篇 |
2008年 | 667篇 |
2007年 | 565篇 |
2006年 | 567篇 |
2005年 | 525篇 |
2004年 | 441篇 |
2003年 | 368篇 |
2002年 | 480篇 |
2001年 | 428篇 |
2000年 | 314篇 |
1999年 | 186篇 |
1998年 | 96篇 |
1997年 | 84篇 |
1996年 | 72篇 |
1995年 | 63篇 |
1994年 | 68篇 |
1993年 | 43篇 |
1992年 | 34篇 |
1991年 | 34篇 |
1990年 | 31篇 |
1989年 | 29篇 |
1988年 | 18篇 |
1987年 | 15篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 17篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1976年 | 6篇 |
1971年 | 4篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
951.
Xing LU Yue WANG Hai Yuan ZHANG Chun Ji NIU* Jia Zuan NI Key Laboratory of Rare Earth Chemistry Physics Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun 《中国化学快报》2001,(9)
With the wide application of rare earth fertilizer and medicines1, more and more rare earths enter into environment, and also into human body via food chain. Now it is very urgent to study the biological effect of rare earths on human health and environment. After entering into human body by whatever route, lanthanide ions are transported to secondary deposition sites mainly via the plasma in the blood stream. So it is very important to study lanthanides speciation in human blood plasma. Becau… 相似文献
952.
De‐Qing Zhang Zhe‐Ming Wang Liang Ding Bin Zhang Wei Xu Dao‐Ben Zhu Chun‐Hua Yan 《中国化学》2001,19(10):966-975
New triphenylamine derivatives 1, 2, 3, and 4 were synthesized and characterized by IR, FAB‐MS, EPR and EA. All of them displayed similar absorption and fluorescence spectra except compound 1, for which a possible explanation was proposed. Quasi‐reversible oxidation waves at about 0.76 V (vs. SCE) and 1.1 V for nitronyl nitroxide and iminyl nitroxide respectively as well as irreversible one at about 1.5 V for triphenylamine group were detected with cyclic voltammetry for compounds 1, 2, 3 and 4. Crystal structures of 2 and 4 were determined by X‐ray diffraction analysis. Their crystal data are as follows: for 2: monoclinic, C2/c, a = 1.69914 (4), b = 1.37435(5), c = 1.24621(5) ran, β= 106.553(2)°, V = 2.7896(2) nm3 Z = 4; for 4: orthorhombic, Pbca, a = 1.95970(6), b = 1.33096(4), c = 4.84691(14) nm, V = 12.6421(7) nm3, Z = 8. Magnetic studies indicated that all of them showed antiferromagnetic properties in solid state, but with strong intermolecular spin‐spin coupling as indicated by the relatively large values of 6, in particular for 4 (θ = ?12 K). Possible spin‐spin interaction mechanism was suggested based on the crystal structures of 2 and 4. 相似文献
953.
Ding Wang Ye Liu Chun‐Yan Hong Cai‐Yuan Pan 《Journal of polymer science. Part A, Polymer chemistry》2005,43(21):5127-5137
Novel hyperbranched poly(amido amine)s containing tertiary amines in the backbones and acryl as terminal groups were synthesized via the Michael addition polymerizations of trifunctional amines with twofold molar diacrylamide. The hyperbranched structures of these poly(amido amine)s were verified by 13C NMR (INVGATE). The polymerization mechanisms were clarified by following the polymerization process with NMR method, and the results show that the reactivity of secondary amine formed in situ is much lower than that of the secondary amine in 1‐(2‐aminoethyl) piperazine (AEPZ) ring and the primary amine. The secondary amine formed in situ was almost kept out of the reaction before the primary and secondary amines in AEPZ were consumed, leading to the formation of the AB2 intermediate, and the further reaction of the AB2 yielded the hyperbranched polymers. The molecular weights and properties of poly(amindo amine)s obtained were characterized by GPC, DSC, and TGA, respectively. Based on the reaction of active acryl groups in the polymers obtained with glucosamine, hyperbranched polymers containing sugar were formed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5127–5137, 2005 相似文献
954.
利用束流能量为116MeV的59Co(35Cl,2p2n)90Mo反应布居90Mo的高自旋态.用10台反康普顿HPGe探测器组成的探测阵列进行γγ符合测量.通过多普勒展宽峰的形状分析测定90Mo高自旋态的寿命.在正宇称衰变系观察到增强的M1跃迁,推断I=13以上是扁椭形变.负宇称高自旋态具有大的B(E2)值,并随自旋增大而起伏变化.正、负宇称态之间的跃迁显示增大的E1跃迁,似有八极关联的可能.但是,90Mo并不处在理论预言的存在八极形变的核区内. 相似文献
955.
In our early researches, lanthanum and cerium could enter plant and bind to porphyrin of chlorophyll to form Ln3+-chllorophyll. La and Ce greatly increase photosystem II (PSII) activity and PSII electron transport rate, and the fluorescence emission peaks of PSII are blue-shifted [1—4]. Do REEs coordinate with PSII reaction center complex in vivo? Moreover, do REEs coordinate with D1(30 kD)/D2(32 kD)/Cytb559 (~9 kD) reaction center complex of site of producing pri-mary reaction-p… 相似文献
956.
957.
958.
We prove two results about the problem of finding the Helly number for line transversals to a family of parallel triangles in the plane: (1) If each three triangles of a family of parallel right triangles are intersected by an ascending (or a descending) line, then there is an ascending (or a descending) line that intersects all 相似文献
959.
960.
Asymmetric borane reduction of achiral ketones in the presence of a chiral oxazaborolidine derived from (−)-ephedrine yielded the corresponding alcohols in optical yields of 41 – 83 % ee. 相似文献