全文获取类型
收费全文 | 37274篇 |
免费 | 9612篇 |
国内免费 | 1434篇 |
专业分类
化学 | 42075篇 |
晶体学 | 343篇 |
力学 | 568篇 |
数学 | 2333篇 |
物理学 | 3001篇 |
出版年
2023年 | 15篇 |
2022年 | 29篇 |
2021年 | 196篇 |
2020年 | 1276篇 |
2019年 | 2605篇 |
2018年 | 1044篇 |
2017年 | 685篇 |
2016年 | 3403篇 |
2015年 | 3553篇 |
2014年 | 3491篇 |
2013年 | 4169篇 |
2012年 | 3064篇 |
2011年 | 2318篇 |
2010年 | 2927篇 |
2009年 | 2887篇 |
2008年 | 2447篇 |
2007年 | 1809篇 |
2006年 | 1509篇 |
2005年 | 1736篇 |
2004年 | 1559篇 |
2003年 | 1424篇 |
2002年 | 2057篇 |
2001年 | 1419篇 |
2000年 | 1329篇 |
1999年 | 394篇 |
1998年 | 88篇 |
1997年 | 74篇 |
1996年 | 68篇 |
1995年 | 57篇 |
1994年 | 47篇 |
1993年 | 48篇 |
1992年 | 33篇 |
1991年 | 31篇 |
1990年 | 29篇 |
1989年 | 39篇 |
1988年 | 20篇 |
1987年 | 27篇 |
1986年 | 30篇 |
1985年 | 39篇 |
1984年 | 39篇 |
1983年 | 37篇 |
1982年 | 24篇 |
1981年 | 26篇 |
1980年 | 21篇 |
1979年 | 19篇 |
1978年 | 25篇 |
1977年 | 26篇 |
1976年 | 32篇 |
1975年 | 24篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
41.
42.
43.
44.
45.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
46.
In this paper we construct an example of a word metric on an infinite cyclic subgroup. This example shows that subexponential
distortion does not obstruct non-trivial growth of connected radii. This answers a question of Gromov [6]. The constructed
metric has other pathological properies. Specifically, its asymptotic cone depends on the choice of ultrafilter and scaling
sequence.
The work has been partially supported by the Swiss National Science Foundation. 相似文献
47.
A novel technique to overcome the long-term drift and hysteresis of a scanning Fabry–Perot filter was developed and applied to wavelength and power monitoring of DWDM system. By using the comb peaks generated by a temperature-stabilized, near threshold-biased Fabry–Perot diode laser as wavelength reference for the scanning Fabry–Perot filter, wavelength and power measurement accuracy of better than ±10 pm and 0.2 dB, respectively, were achieved. 相似文献
48.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
49.
It is proved that the variety of relevant disjunction lattices has the finite embeddability property. It follows that Avron's relevance logic RMI min has a strong form of the finite model property, so it has a solvable deducibility problem. This strengthens Avron's result that RMI min is decidable. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
50.
Yu-Soo Lee Hyun-Ju Chung Jong-Han Joung Eung-Jo Kim Hee-Je Kim 《Optics & Laser Technology》2004,36(1):461-61
We describe the pulse forming of pulsed CO2 laser using multi-pulse superposition technique. Various pulse shapes, high duty cycle pulse forming network (PFN) are constructed by time sequence. This study shows a technology that makes it possible to make various long pulse shapes by activating SCRs of three PFN modules consecutively at a desirable delay time with the aid of a PIC one-chip microprocessor. The power supply for this experiment consists of three PFN modules. Each PFN module uses a capacitor, a pulse forming inductor, a SCR, a high voltage pulse transformer, and a bridge rectifier on each transformer secondary. The PFN modules operate at low voltage by driving the primary of HV pulse transformer. The secondary of the transformer has a full-wave rectifier, which passes the pulse energy to the load in a continuous sequence.We investigated various long pulse shapes as different trigger time intervals of SCRs among three PFN modules. As a result, we could obtain laser beam with various pulse shapes and durations from about 250 to 1000 μs. 相似文献