全文获取类型
收费全文 | 12887篇 |
免费 | 3319篇 |
国内免费 | 894篇 |
专业分类
化学 | 3199篇 |
晶体学 | 560篇 |
力学 | 170篇 |
综合类 | 76篇 |
数学 | 121篇 |
物理学 | 12974篇 |
出版年
2024年 | 46篇 |
2023年 | 99篇 |
2022年 | 265篇 |
2021年 | 274篇 |
2020年 | 275篇 |
2019年 | 225篇 |
2018年 | 265篇 |
2017年 | 425篇 |
2016年 | 480篇 |
2015年 | 472篇 |
2014年 | 755篇 |
2013年 | 1188篇 |
2012年 | 913篇 |
2011年 | 882篇 |
2010年 | 650篇 |
2009年 | 803篇 |
2008年 | 991篇 |
2007年 | 904篇 |
2006年 | 869篇 |
2005年 | 782篇 |
2004年 | 675篇 |
2003年 | 618篇 |
2002年 | 578篇 |
2001年 | 544篇 |
2000年 | 493篇 |
1999年 | 432篇 |
1998年 | 366篇 |
1997年 | 345篇 |
1996年 | 270篇 |
1995年 | 265篇 |
1994年 | 224篇 |
1993年 | 164篇 |
1992年 | 136篇 |
1991年 | 88篇 |
1990年 | 65篇 |
1989年 | 57篇 |
1988年 | 48篇 |
1987年 | 41篇 |
1986年 | 27篇 |
1985年 | 28篇 |
1984年 | 23篇 |
1983年 | 7篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1970年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
研究了利用N-乙酰-L-谷氨酸为拆分试剂,成功的对氯化3-氰-2-羟丙基三甲胺进行光学拆分,一次拆分光学纯度为92%,产率为37%;二次拆分光学纯度达95%,产率为29.1%。 相似文献
942.
塑料光纤的微分模延迟数据对研究塑料光纤的色散特性具有非常重要的意义。采用频域相移法测量了不同长度的两种折射率分布塑料光纤:阶跃型塑料光纤(SI—POF)和渐变型塑料光纤(GI—POF)的微分模延迟曲线。实验结果表明,由于短光纤可以忽略模式耦合和模式损耗,1m塑料光纤的微分模延迟测量值与理论计算值吻合得非常好。因此,频域相移法可以简单、方便、精确地测量塑料光纤的微分模延迟。此外,通过比较不同长度塑料光纤的微分模延迟曲线的变化,可在一定程度上分析光纤中存在的模式耦合。 相似文献
943.
This article compares the performance of WDM lightpath protection and IP LSP protection schemes for IP-over-WDM networks. A mathematical formulation of the maximum throughput problem is presented and analytical expressions for recovery time are derived for both schemes. The throughputs and recovery times are analyzed and compared. Results show that the IP LSP protection scheme presents higher throughputs then WDM lightpath protection. The IP LSP protection scheme, providing individual IP LSP protection has, however, scalability problems. This scheme presents high recovery times when a failure affects many lightpaths and many hops are allowed for the primary routes of IP LSPs. 相似文献
944.
利用液芯光纤技术研究了不同浓度的β-Carotene的CS2溶液的吸收与荧光的特性对CS2的一、二阶Stokes谱线阈值的影响.实验发现随溶液浓度(10-8—10-6 mol/L)增加,CS2的一阶Stokes谱线的激发阈值相对变高;并且与纯CS2芯液的受激拉曼散射相比较,在低抽运能量激发下,就观察到CS2的二阶Stokes谱线.这主要是由于在CS2的受激拉曼谱线产生的过程中,β-Carotene的CS2溶液的吸收和荧光共同影响了CS2的一、二阶Stokes谱线的阈值.我们进行了理论上的拟合与分析,其结果与实验符合很好.
关键词:
2受激拉曼散射阈值')" href="#">CS2受激拉曼散射阈值
液芯光纤
吸收与荧光 相似文献
945.
手性化合物绝对构型的确定一直是有机化学特别是手性药物合成研究过程中经常遇到的问题之一. 利用密度泛函DFT/B3LYP量子化学计算方法, 通过计算两种已知旋光度分子的旋光度, 确认计算条件和验证计算结果的可靠性, 并将此方法应用于Soman旋光度的计算. 结合文献报道的Soman分子实验旋光度测定结果, 首次采用理论计算方法确定了梭曼(Soman)分子四个异构体的绝对构型, 分别为P(R),C(S)-Soman→P(+)C(+), P(R),C(R)-Soman→P(+)C(-), P(S),C(S)-Soman→P(-)C(+), P(S),C(R)-Soman→P(-)C(-). 相似文献
946.
Andreas Manz Elisabeth Verpoorte Carlo S. Effenhauser Norbert Burggraf Daniel E. Raymond D. Jed Harrison H. Michael Widmer 《Journal of separation science》1993,16(7):433-436
Miniaturization of separation columns implies equally reduced vol- umes of injectors, detectors, and the connecting channels. Planar chip technology provides a powerful means for the fabrication of micron-sized structures such as channels. This is demonstrated by two examples. An optical absorbance detector chip exhibits the expected behavior of a 1 mm optical path length cell despite its volume of 1 nL. A capillary electrophoresis device allows integrated injections of 100 pL samples, efficiencies of 70,000 to 160,000 theoretical plates in 10 to 20 seconds, and external laser-induced fluorescence detection at any capillary length of choice between 5 and 50 mm. 相似文献
947.
介绍了以FPGA为主控芯片,以光纤为通讯媒介的视频信号数字通信实验装置的设计实现过程,并对电路各个模块的功能及实现加以说明.电路在Altium Designer中设计完成,采用分模块式的设计,结构清晰,易于实现.在QuartusⅡ环境下用VerilogHDL语言进行编程并对程序进行仿真.该装置已做成了实体,可以实现视频信号的传输. 相似文献
948.
Ying-Tung Chen Kris Naessens Roel Baets Yunn-Shiuan Liao Ampere A. Tseng 《Optical Review》2005,12(6):427-441
For many years, the development of effective ablation or laser machining techniques for making micro-optical components has
been the key factor in the birth of new photonic devices and systems. In this article, the ablation characteristics of two
types of the most important transparent materials, transparent polymers and glasses, are studied. Simple shaped microcavities
are first machined for studying the fundamental ablation parameters, including threshold fluence, effective absorption coefficient,
and ablation rate. In studying polymer ablation, five standard grades and five proprietary polymeric compounds are selected.
Ablation techniques using these transparent polymers for making arrayed ferrules and curved microlenses are presented. Applications
of these ablated microstructures for optical fiber connectors, optical fiber coupling and alignment, and transparent chip
encapsulants, are introduced and demonstrated with emphasis on the quality of the ablated profiles and dimensions to satisfy
the required performance. In glass ablation, borosilicate glasses are considered and their associated ablation behaviors are
studied. The procedures to ablate glass-based arrayed microstructures with flat and curved surfaces are described. The utilizations
of these arrayed microstructures for optical waveguide, wave absorber, and beam guider, are specifically discussed. Finally,
concluding remakes for future trends are presented. 相似文献
949.
950.
Measurement Accuracy in Phase-Shifting Point Diffraction Interferometer with Two Optical Fibers 总被引:1,自引:0,他引:1
Toshiaki Matsuura Satoru Okagaki Takaaki Nakamura Yasushi Oshikane Haruyuki Inoue Motohiro Nakano Toshihiko Kataoka 《Optical Review》2007,14(6):401-405
A phase-shifting point diffraction interferometer (PS/PDI) with point sources of two single mode optical fibers has been developed,
which will be appropriate for the surface figure measurement of large aperture optics on a sub-nanometer scale. To reduce
the measurement error factors, a fiber optic plate (FOP) is used as a projection plane for interference pattern. Errors caused
by imperfection of optical alignment, such as position of point sources and tilt of FOP, are minimized by analyzing the measured
phase data with an original method. Measurement accuracy in the PS/ PDI is estimated with the interference pattern produced
by the two optical fiber sources. If inhomogeneity of the FOP and a systematic error of the PS/PDI are eliminated, the measurement
accuracy of the present system is estimated to be less than 4nm P-V and 0.7nm rms, respectively, at a measurement wavelength
of 632.8 nm. 相似文献