全文获取类型
收费全文 | 13124篇 |
免费 | 2297篇 |
国内免费 | 1419篇 |
专业分类
化学 | 9088篇 |
晶体学 | 122篇 |
力学 | 884篇 |
综合类 | 88篇 |
数学 | 1614篇 |
物理学 | 5044篇 |
出版年
2024年 | 45篇 |
2023年 | 280篇 |
2022年 | 475篇 |
2021年 | 508篇 |
2020年 | 532篇 |
2019年 | 474篇 |
2018年 | 462篇 |
2017年 | 400篇 |
2016年 | 575篇 |
2015年 | 636篇 |
2014年 | 734篇 |
2013年 | 979篇 |
2012年 | 1123篇 |
2011年 | 1149篇 |
2010年 | 798篇 |
2009年 | 735篇 |
2008年 | 818篇 |
2007年 | 764篇 |
2006年 | 684篇 |
2005年 | 562篇 |
2004年 | 416篇 |
2003年 | 348篇 |
2002年 | 320篇 |
2001年 | 280篇 |
2000年 | 236篇 |
1999年 | 278篇 |
1998年 | 262篇 |
1997年 | 191篇 |
1996年 | 214篇 |
1995年 | 213篇 |
1994年 | 183篇 |
1993年 | 160篇 |
1992年 | 131篇 |
1991年 | 142篇 |
1990年 | 144篇 |
1989年 | 108篇 |
1988年 | 92篇 |
1987年 | 79篇 |
1986年 | 59篇 |
1985年 | 62篇 |
1984年 | 28篇 |
1983年 | 33篇 |
1982年 | 26篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1974年 | 6篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
982.
983.
本文探讨具有违约风险的人寿保险的最优定价.我们从Black-Scholes的期权定价模型出发,考虑风险管理和准备金的要求,根据一次支付和均衡支付这两种不同的假设分别建立两个优化模型,并且借助于优化技术获得最优解.数量化分析结果表明,两个模型的最优价格对于利息率参数以及非索赔成本的变化都不敏感.这说明这两个模型是稳定的,而且是实用的. 相似文献
984.
Changzhi Han Peihua Dong Haoran Tang Peiyun Zheng Chong Zhang Feng Wang Fei Huang Jia-Xing Jiang 《Chemical science》2021,12(5):1796
The design and synthesis of conjugated semiconducting polymers for photocatalytic hydrogen evolution have engendered intense recent interest. However, most reported organic polymer photocatalysts show a relatively broad band gap with weak light absorption ability in the visible light region, which commonly leads to a low photocatalytic activity under visible light. Herein, we synthesize three novel dithieno[3,2-b:2′,3′-d]thiophene-S,S-dioxide (DTDO) containing conjugated polymer photocatalysts by a facile C–H arylation coupling polymerization reaction. The resulting polymers show a broad visible light absorption range up to 700 nm and a narrow band gap down to 1.81 eV due to the introduction of the DTDO unit. Benefiting from the donor–acceptor polymer structure and the high content of the DTDO unit, the three-dimensional polymer PyDTDO-3 without the addition of a Pt co-catalyst shows an attractive photocatalytic hydrogen evolution rate of 16.32 mmol h−1 g−1 under visible light irradiation, which is much higher than that of most reported organic polymer photocatalysts under visible light.Narrow band gap conjugated polymer photocatalysts containing dithieno[3,2-b:2′,3′-d]thiophene-S,S-dioxide show an attractive photocatalytic hydrogen evolution rate of 16.32 mmol h−1 g−1 under visible light irradiation. 相似文献
985.
The first phytochemical investigation on stems of Mitrephora thorelii led to the isolation of three new lignanamides, thoreliamides A–C ( 1 – 3 ), and a new sesquiterpenoid, thorelinin ( 4 ), together with ten known compounds. The structures of the new compounds were established on the basis of extensive spectroscopic analyses. Thoreliamide C is the first trimer derived from cinnamic acid amide units. 相似文献
986.
Starting from one fullerene, the three geometric transformations, cap, face dual and edge dual produce series of carbon clusters and deltahedra. The geometric relation between these polyhedra implies that their topological matrices and eigenvalue spectra must be relative. We have developed a matrix algebra method to research some polyhedra with high symmetry and one kind, two or three kinds of equivalent vertices such as C60(Ih), resolve their exact eigenvalues, and proved this point. 相似文献
987.
We investigate the confinement properties of bounded, nonnegative, compactly supported vortices of axisymmetric incompressible Euler flows without swirl. We show that along one direction of the symmetry axis, its support can grow no faster than O[(t log t)1/2]. The rate at which it approaches the symmetry axis is also estimated. Together with the result of Maffei–Marchioro on the radial growth rate of the support, it is contained in a slowly expanding tubular region. The techniques of the above‐mentioned authors, Iftimie–Lopes–Nussenzveig and Iftimie–Sideris–Gamblin, are used. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
988.
Gang‐Yin Shi Xue‐Zhi Tang Cai‐Yuan Pan 《Journal of polymer science. Part A, Polymer chemistry》2008,46(7):2390-2401
The tadpole‐shaped amphiphilic copolymers with cyclic polystyrene as the head and a linear poly(N‐isopropylacrylamide) as the tail have been successfully synthesized by combination of reversible addition‐fragmentation chain transfer (RAFT) polymerization and “click” reaction. The synthesis involves two main steps: (1) preparation of a linear acetylene‐terminated PNIPAAM‐b‐PS with a side azido group anchored at the junction between two blocks; (2) intramolecular cyclization reaction to produce the cyclic PS block using “click” chemistry under high dilution. The structures, molecular weights, and molecular weight distributions of the resulted intermediates and the target polymers were characterized by their 1H NMR, FTIR, and gel permeation chromatography. The difference of surface property between tadpole‐shaped polymer and its linear precursor was observed, and the water contact angles on the former surface are larger than that of the latter surface. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2390–2401, 2008 相似文献
989.
H. Luo D.Y. Tang G.Q. Xie H.J. Zhang L.J. Qin H.H. Yu L.Y. Ng L.J. Qian 《Optics Communications》2008,281(21):5382-5384
Passive mode-locking of a diode pumped Yb-doped GdVO4 crystal laser was demonstrated for the first time to our knowledge. The laser was mode-locked at the wavelength of 1019.1 nm and had an average output power of 1.01 W. The mode-locked pulse duration was 3.1 ps. The laser was end-pumped by a high-power fiber pigtailed laser diode bar and the mode-locking was enabled by a semiconductor saturable absorber mirror (SESAM). 相似文献
990.