全文获取类型
收费全文 | 72699篇 |
免费 | 7478篇 |
国内免费 | 7180篇 |
专业分类
化学 | 30807篇 |
晶体学 | 524篇 |
力学 | 2997篇 |
综合类 | 336篇 |
数学 | 5659篇 |
物理学 | 18358篇 |
综合类 | 28676篇 |
出版年
2024年 | 247篇 |
2023年 | 990篇 |
2022年 | 1610篇 |
2021年 | 1696篇 |
2020年 | 1711篇 |
2019年 | 1513篇 |
2018年 | 1405篇 |
2017年 | 1401篇 |
2016年 | 2063篇 |
2015年 | 2228篇 |
2014年 | 2777篇 |
2013年 | 3377篇 |
2012年 | 4023篇 |
2011年 | 5834篇 |
2010年 | 3668篇 |
2009年 | 3972篇 |
2008年 | 3443篇 |
2007年 | 3230篇 |
2006年 | 3002篇 |
2005年 | 2871篇 |
2004年 | 4608篇 |
2003年 | 3354篇 |
2002年 | 2895篇 |
2001年 | 2297篇 |
2000年 | 1835篇 |
1999年 | 2410篇 |
1998年 | 2224篇 |
1997年 | 2244篇 |
1996年 | 1749篇 |
1995年 | 1455篇 |
1994年 | 1583篇 |
1993年 | 1883篇 |
1992年 | 1656篇 |
1991年 | 1379篇 |
1990年 | 1333篇 |
1989年 | 1096篇 |
1988年 | 763篇 |
1987年 | 548篇 |
1986年 | 340篇 |
1985年 | 239篇 |
1984年 | 147篇 |
1983年 | 82篇 |
1982年 | 70篇 |
1981年 | 38篇 |
1980年 | 19篇 |
1979年 | 12篇 |
1977年 | 5篇 |
1957年 | 3篇 |
1938年 | 3篇 |
1893年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
揭示了城市技术创新系统和城乡统筹发展的内涵,并在技术创新、增长极和区域经济等理论框架下阐述了城市技术创新与城乡统筹发展的关系,进而提出城市技术创新促进城乡统筹的路径。 相似文献
62.
63.
设 A是对称正定矩阵,λ_1是 A 的最大或最小特征值,χ_1是对应的特征向量.{zk}是用共轭斜量法求解方程组 Αχ=b时的近似解序列,ei=A~(_1)b-zi,本文给出了|x_1~Tei|较合理的上界估计式。从而为分析预处理共轭斜量法提供了进一步的理论基础。 相似文献
64.
A method for fabricating well-dispersed nanowire suspension has been demonstrated in the paper. Thin gold nanowires were prepared by template synthesis, and then functionalized with sulphonate group-terminated thiols before suspended in different solvents. The degree of aggregation of the obtained suspension was evaluated with transmission electron microscopy (TEM) and UV-vis spectroscopy. It was found that the degree of aggregation was predominated by the solvents, and the best degree of dispersion was obtained when isopropyl alcohol (IPA) was used as the solvent. The gold nanowires from the suspension can be selectively assembled onto chemically patterned substrates. This well-dispersed nanowire suspension is potentially useful for fabricating novel nanodevices. 相似文献
65.
Some new oscillation criteria are established for a second order neutral delay differential equations. These results improve oscillation results of Y.V. Rogo-vchenko for the retarded delay differential equations. The relevance of our theorems is illustrated with two carefully selected examples. 相似文献
66.
针对柱面注浆方式,研究了有关渗透注浆的单孔复注及不同方式布孔时多孔注浆的相互影响等问题,推导出一些有价值的岩体注浆理论公式,可用于指导现场注浆工程的设计与施工. 相似文献
67.
Kosuke Morita Kouji Morimoto Daiya Kaji Yu Liang Zhao Atsushi Yoshida Toshimi Suda Akira Yoneda Tetsuya Ohnishi Hiromitsu Haba Eiji Ideguchi Hu Shan Xu Tao Zheng Hisaaki Kudo Keisuke Sueki Kenji Katori Isao Tanihata 《Acta Physica Hungarica A》2004,19(1-2):53-60
A gas-filled type of recoil separator for heavy element research was installed at an experimental hall of RIKEN Linear Accelerator facility to realize getting higher intensity of primary beam and long beam time. Performance of the separator was studied using target recoils and various nuclear reactions. The results show the high performance of the separator for heave element research. As an application of the GARIS, production and identification of an isotope of the 110th element 271[110] have been performed using the 208Pb(64Ni,1n)271[110] reaction. Three decay chains coincide well both in decay times and energies with the ones reported by the group of SHIP experiment at GSI, Germany. Our results provide a confirmation of the synthesis of an isotope 271[110] of element 110. 相似文献
68.
Qi Wang Huaxiang Yang Zhiqiang Fan Hong Xu 《Journal of polymer science. Part A, Polymer chemistry》2004,42(5):1093-1099
Ethylisobutylaluminoxane (EBAO) and its analogues were synthesized by a reaction between an triethylaluminum (Et3Al)/triisobutylaluminum (i‐Bu3Al) mixture and 4‐fluorobenzeneboronic acid, phenylboronic acid, or n‐butaneboronic acid and subsequent hydrolysis with water. They were used as cocatalysts in ethylene polymerization catalyzed by an iron complex {[(ArN?C(Me))2C5H3N]FeCl2, where Ar is 2,6‐diisopropylphenyl}. Polyethylene with a high molecular weight and a narrow molecular weight distribution was prepared with modified EBAOs, and the performance of the iron complex at high polymerization temperatures was greatly improved. The activators for the iron complex also affected the polymerization activity and the molecular weight of the resultant polyethylene. It was suggested that the stereo and electronic effects of the substitute groups of aluminoxane contributed to the improved performance of the new activators. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1093–1099, 2004 相似文献
69.
A reliable method is presented for the chiral separation of three basic drugs (mexiletine, chlorpheniramine and propranolol) with serum albumins (human and porcine, HSA and PSA) as chiral selectors by capillary electrophoresis in combination with the partial filling technique. Based on the systematic optimization of operation variables, the chiral separation of mexiletine, chlorpheniramine and propranolol was achieved in the pH 7.4 phosphate buffer by using HSA, PSA and PSA as selectors, respectively. The chiral recognition ability of HSA and PSA was compared. HSA and PSA show a different chiral recognition ability for each of the three drugs. In addition, the association constants between enantiomeric drugs and proteins were determined to be 2.00 and 3.80 x 10(2) M(-1) for mexiletine and HSA, 0.59 and 1.12 x 10(3) M(-1) for chlorpheniramine and PSA, and 0.87 and 1.42 x 10(3) M(-1) for propranolol and PSA. The method for the chiral separation and determination of association constants possesses the advantages of simple performance, effective avoiding of the interference of the UV detection from protein, and lowering of the reagent consumption. 相似文献
70.
A hybrid cluster complex, formed by chelating a chromogenic ligand to a [2Fe-2S] cluster, sensitively exhibited differential colorimetric responses towards Hg2+, Cd2+, Cr3+, Pb2, Sn2+, Cu2+, Zn2+, Fe3+ and Co2+ in water at physiological pH. Speciation of some of these metal elements, such as Cr(III) and Sn(IV), was also studied by UV/Vis absorption. 相似文献