全文获取类型
收费全文 | 640376篇 |
免费 | 6676篇 |
国内免费 | 1489篇 |
专业分类
化学 | 323495篇 |
晶体学 | 9445篇 |
力学 | 32005篇 |
综合类 | 16篇 |
数学 | 85053篇 |
物理学 | 198527篇 |
出版年
2021年 | 5779篇 |
2020年 | 6425篇 |
2019年 | 7247篇 |
2018年 | 9957篇 |
2017年 | 9902篇 |
2016年 | 14071篇 |
2015年 | 7938篇 |
2014年 | 13176篇 |
2013年 | 28530篇 |
2012年 | 22474篇 |
2011年 | 27073篇 |
2010年 | 20261篇 |
2009年 | 20333篇 |
2008年 | 25489篇 |
2007年 | 25088篇 |
2006年 | 23035篇 |
2005年 | 20369篇 |
2004年 | 19128篇 |
2003年 | 17089篇 |
2002年 | 17258篇 |
2001年 | 18525篇 |
2000年 | 14324篇 |
1999年 | 11051篇 |
1998年 | 9560篇 |
1997年 | 9215篇 |
1996年 | 8714篇 |
1995年 | 7865篇 |
1994年 | 7824篇 |
1993年 | 7603篇 |
1992年 | 8188篇 |
1991年 | 8557篇 |
1990年 | 8281篇 |
1989年 | 8120篇 |
1988年 | 7918篇 |
1987年 | 7871篇 |
1986年 | 7392篇 |
1985年 | 9291篇 |
1984年 | 9523篇 |
1983年 | 7763篇 |
1982年 | 8007篇 |
1981年 | 7711篇 |
1980年 | 7213篇 |
1979年 | 7919篇 |
1978年 | 8126篇 |
1977年 | 8128篇 |
1976年 | 8119篇 |
1975年 | 7507篇 |
1974年 | 7361篇 |
1973年 | 7475篇 |
1972年 | 5721篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
982.
We show that using ionic liquids as reagents in conjunction with microwave heating it is possible to prepare primary alkyl halides from the corresponding alcohols rapidly. Using ionic liquids as solvents in conjunction with microwave heating it is possible to prepare aryl nitriles from the corresponding aryl bromides or iodides. The scope and limitations of using microwave-promotion as a tool in these reactions is discussed. 相似文献
983.
984.
A. Sanusi M. Z. A. Yahya S. Navaratnam W. J. Basirun Y. Alias N. S. Mohamed A. K. Arof 《Ionics》2003,9(3-4):253-257
In this study, lead sulphide (PbS) was prepared by the chemical bath deposition technique. The sample was characterized by
X-ray diffraction (XRD), Energy Dispersive Analysis of X-rays (EDAX) and cyclic voltammetry. EDAX spectrum shows peaks attributable
to lead and sulphur. The EDAX analysis also shows that the prepared sample is stoichiometric. Cyclic voltammetry experiments
were recorded at 100 mV·s−1 and 400 mV·s−1 scan rates. Results show that the rate controlling electrochemical reaction is electron transfer. The presence of redox waves
shows that the lithium intercalation and deintercalation can occur as a result of lattice expansion in PbS. There were no
differences in the PbS XRD data before and after the cyclic voltammetry experiments indicating that the PbS structure is not
modified upon lithium ion intercalation and deintercalation in PbS. The discharge characteristics for 35 cycles of the cell
using the LiCoO2/PbS couple is presented indicating the possible development of such materials as anode in lithium ion cells. 相似文献
985.
Multilayer wave-guiding structures comprising transversely magnetized ferrites are studied. A numerical theoretical model
is constructed with the Galerkin method. An experimental investigation technique is developed. Theoretical and experimental
results are found to be in good agreement. Such structures offer a high phase activity and may provide a basis for small-size
millimeter-wave phase shifters and a new class of antenna systems, namely, integrated phased arrays. 相似文献
986.
V. Bradnova M. M. Chernyavsky L. Just S. P. Kharlamov A. D. Kovalenko M. Haiduc K. A. Kotel’nikov V. A. Krasnov V. G. Larionova F. G. Lepekhin A. I. Malakhov G. I. Orlova N. G. Peresadko N. G. Polukhina P. A. Rukoyatkin V. V. Rusakova N. A. Salmanova B. B. Simonov S. Vokal P. I. Zarubin 《Physics of Atomic Nuclei》2003,66(9):1646-1650
A physical program of irradiation of emulsions in beams of relativistic nuclei named the BECQUEREL Project is reviewed. It is destined to study in detail the processes of relativistic fragmentation of light radioactive and stable nuclei. The expected results would make it possible to answer some topical questions concerning the cluster structure of light nuclei. Owing to the best spatial resolution, the nuclear emulsions would enable one to obtain unique and evident results. The most important irradiations will be performed in the secondary beams of He, Be, B, C, and N radioactive nuclei formed on the basis of JINR Nuclotron beams of stable nuclei. We present results on the charged state topology of relativistic fragmentation of the 10B nucleus at low energy-momentum transfers as the first step of the research. 相似文献
987.
988.
989.
In previous papers by the present author, a machinery for calculating automorphisms, constructing invariants, and classifying real submanifolds of a complex manifold was developed. The main step in this machinery is the construction of a “nice” model surface. The nice model surface can be treated as an analog of the osculating paraboloid in classical differential geometry. Model surfaces suggested earlier possess a complete list of the desired properties only if some upper estimate for the codimension of the submanifold is satisfied. If this estimate fails, then the surfaces lose the universality property (that is, the ability to touch any germ in an appropriate way), which restricts their applicability. In the present paper, we get rid of this restriction: for an arbitrary type (n,K) (where n is the dimension of the complex tangent plane, and K is the real codimension), we construct a nice model surface. In particular, we solve the problem of constructing a nondegenerate germ of a real analytic submanifold of a complex manifold of arbitrary given type (n,K) with the richest possible group of holomorphic automorphisms in the given class. 相似文献
990.
Benjamin E. Blass Anil Srivastava Amy L. Faulkner James M. Ridgeway 《Tetrahedron letters》2004,45(6):1275-1277
The solid-phase synthesis of a series of imidazo[1,2-b]pyrazol-2-ones, an interesting 5,5-fused ring system, based on diverse set of hydrazine acids and malanonitriles is described. The method involves formation of 5-aminopyrazoles on solid support and subsequent cyclizative cleavage off the resin. Compounds were obtained in acceptable to excellent yields and are suitable for biological evaluation without further purification. 相似文献