全文获取类型
收费全文 | 43697篇 |
免费 | 3536篇 |
国内免费 | 2306篇 |
专业分类
化学 | 30739篇 |
晶体学 | 529篇 |
力学 | 1869篇 |
综合类 | 188篇 |
数学 | 4095篇 |
物理学 | 12119篇 |
出版年
2023年 | 390篇 |
2022年 | 722篇 |
2021年 | 984篇 |
2020年 | 1022篇 |
2019年 | 1041篇 |
2018年 | 797篇 |
2017年 | 789篇 |
2016年 | 1483篇 |
2015年 | 1345篇 |
2014年 | 1673篇 |
2013年 | 2692篇 |
2012年 | 3404篇 |
2011年 | 3671篇 |
2010年 | 2388篇 |
2009年 | 2092篇 |
2008年 | 2834篇 |
2007年 | 2601篇 |
2006年 | 2474篇 |
2005年 | 2307篇 |
2004年 | 1959篇 |
2003年 | 1598篇 |
2002年 | 1651篇 |
2001年 | 1160篇 |
2000年 | 1005篇 |
1999年 | 721篇 |
1998年 | 549篇 |
1997年 | 553篇 |
1996年 | 592篇 |
1995年 | 494篇 |
1994年 | 461篇 |
1993年 | 453篇 |
1992年 | 425篇 |
1991年 | 344篇 |
1990年 | 278篇 |
1989年 | 242篇 |
1988年 | 226篇 |
1987年 | 181篇 |
1986年 | 160篇 |
1985年 | 234篇 |
1984年 | 146篇 |
1983年 | 133篇 |
1982年 | 144篇 |
1981年 | 112篇 |
1980年 | 89篇 |
1978年 | 85篇 |
1977年 | 87篇 |
1976年 | 98篇 |
1975年 | 104篇 |
1974年 | 85篇 |
1973年 | 108篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
991.
Palumbo Anthony V. Lee S. Y. Boerman Patrice 《Applied biochemistry and biotechnology》1994,45(1):811-822
Applied Biochemistry and Biotechnology - EDTA degradation by anAgrobacterium sp. has been examined by quantifying14C-labeled CO2 produced from iron-[2-14C] EDTA and by measured loss of nonlabeled... 相似文献
992.
993.
In a capacitively coupled discharge with external electrodes, He, H_2, N_2 or Ar were used as plasmagas, polymerization of octafluorocyclobutane was carried out under different conditions by varyingdischarge power, pressure, plasma gas and plasma-gas/monomer ratio. Structure of polymerizedproducts was characterized by IR spectroscopy and ESCA measurement. It was found that therewere six elements in the products, i.e. C, F, Si, O, N and H. The probably existed groups in poly-mers wer investigated. By analyzing the resolved peaks of C_(1S) region in ESCA spectra, effect of thereaction conditions on degree of branching of the polymerized products and the relationship of thepolymer structure wth the mechanism of the competitive ablation and polymerization process werestudied. In addition, polymer deposition process occurring in glow discharge was discussed. 相似文献
994.
995.
利用波长为266nm的激光光解CHBr3产生CH自由基,其与NO反应作为NCO自由基的来源.在298K,总压2660Pa的条件下,采用激光诱导荧光的方法,研究了NCO自由基与SO2、CS2的反应.得到了NCO自由基与SO2、CS2双分子反应速率常数分别为(1.8±0.3)×10-11和(3.1±0.4)×10-12cm3·molecule-1·s-1.对这两个反应在B3LYP/6-31 G(d)的水平上进行理论研究的结果表明,NCO自由基与SO2、CS2的反应是加成反应,其机理是NCO自由基中的N原子攻击反应物的中心原子,得到加成产物. 相似文献
996.
997.
A comparison between the construction of symmetry-correlation diagrams and the perturbation method for studying chemical reactions is carried out. The perturbation method consists of decomposing the system Hamiltonian H into a sum, H = H0 + H′. Various symmetry correlation schemes appearing in the literature may be explained by the nonuniqueness of the decomposition scheme. All symmetry selection rules may be viewed as the varieties. By examining the symmetry-correlation diagrams, processes under investigation may be called “forbidden” or “allowed,” depending on the topological feature. Of particular importance is the topology associated with the “avoided crossing.” By making the comparison, we can establish the correspondence of the two methods and conclude that the perturbation order furnishes the origin of the “forbiddenness” of a process. 相似文献
998.
An attempt to classify various types of avoided surface crossings originally discussed by Salem and co-workers is presented. From the present scheme, an order-of-forbiddenness criterion regarding reactivity is established from a consideration of electron and orbital counting. Since the new classification is qualitatively related to the energy gap created in the avoided crossing, the classification appears to be more systematic and informative. Energy transfer processes involved in electronically excited states may also be rationalized by such an application. Three major mechanistic types are distinguished: concerted two-electron process, concerted one-electron process, and stepwise one-electron process involving an ionic-pair intermediate. 相似文献
999.
A core-shell structure was found in AM SURE™ resin, in which most amino groups were located at the skin layer. The AM SURE™ resin revealed better synthetic efficiency, compared to the noncore-shell type resin in the synthesis of the fragment 65-74 of acyl carrier protein, the fragment 27-35 of HIV (human immunodeficiency virus) fusion inhibitor (T-20) and the Jung-Redemann 10-mer. 相似文献
1000.
[formula: see text] S-Nitrosoglutathione oxidized 4-substituted Hantzsch 1,4-dihydropyridines in CH3CN/H2O or CH3CN/phosphate aqueous buffer solution to give aromatic products in various yields. 相似文献