全文获取类型
收费全文 | 14660篇 |
免费 | 1740篇 |
国内免费 | 1409篇 |
专业分类
化学 | 7166篇 |
晶体学 | 92篇 |
力学 | 436篇 |
综合类 | 103篇 |
数学 | 1065篇 |
物理学 | 3761篇 |
综合类 | 5186篇 |
出版年
2024年 | 47篇 |
2023年 | 267篇 |
2022年 | 465篇 |
2021年 | 465篇 |
2020年 | 521篇 |
2019年 | 456篇 |
2018年 | 403篇 |
2017年 | 388篇 |
2016年 | 557篇 |
2015年 | 595篇 |
2014年 | 781篇 |
2013年 | 864篇 |
2012年 | 1098篇 |
2011年 | 1072篇 |
2010年 | 766篇 |
2009年 | 742篇 |
2008年 | 922篇 |
2007年 | 855篇 |
2006年 | 741篇 |
2005年 | 659篇 |
2004年 | 484篇 |
2003年 | 390篇 |
2002年 | 405篇 |
2001年 | 386篇 |
2000年 | 347篇 |
1999年 | 411篇 |
1998年 | 355篇 |
1997年 | 324篇 |
1996年 | 308篇 |
1995年 | 303篇 |
1994年 | 258篇 |
1993年 | 193篇 |
1992年 | 184篇 |
1991年 | 136篇 |
1990年 | 142篇 |
1989年 | 124篇 |
1988年 | 121篇 |
1987年 | 73篇 |
1986年 | 66篇 |
1985年 | 51篇 |
1984年 | 15篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
Jones DJ Holman KW Notcutt M Ye J Chandalia J Jiang LA Ippen EP Yokoyama H 《Optics letters》2003,28(10):813-815
Using high-bandwidth feedback, we have synchronized the pulse train from a mode-locked semiconductor laser to an external optical atomic clock signal and achieved what is to our knowledge the lowest timing jitter to date (22 fs, integrated from 1 Hz to 100 MHz) for such devices. The performance is limited by the intrinsic noise of the phase detector used for timing-jitter measurement. We expect such a highly stable device to play an important role in fiber-network-based precise time/frequency distribution. 相似文献
992.
Various analogs of NMR and MRI are now technically possible in optics; specifically, high-resolution laser-pulse shaping and complex pulse sequence generation with well-defined phase shifts has been demonstrated. Here we summarize this technology and discuss the potential for these methods to enhance optical functional imaging, competing with (and surpassing?) what is possible by functional MRI. 相似文献
993.
Time-of-flight spectra were collected for 2.5 keV 7Li+ backscattered from Fe surfaces covered with submonolayers of iodine. Li singly scattered from the adatoms has a consistently larger neutral fraction than for scattering from the substrate, implying a region of positive charge atop the iodine. The neutral fraction decreases for off-normal exit angles, indicating a nonuniform charge distribution around the polarizable adsorbates. This demonstrates that ion scattering can image the internal electronic structure of an adatom and provides an explanation for anomalous work function changes. 相似文献
994.
PNA for one-base differentiating protection of DNA from nuclease and its use for SNPs detection 总被引:2,自引:0,他引:2
Komiyama M Ye S Liang X Yamamoto Y Tomita T Zhou JM Aburatani H 《Journal of the American Chemical Society》2003,125(13):3758-3762
By the combination of peptide nucleic acid (PNA) with single-stranded DNA specific nucleases, alteration of a single base to another in DNA has been detected with high accuracy. Only the DNAs in DNA/PNA duplexes involving a mismatch are efficiently hydrolyzed by these enzymes, whereas fully matching sequences are kept intact. This difference is visually scored by adding 3,3'-diethylthiadicarbocyanine, which changes its color from blue to purple upon binding to DNA/PNA duplexes. These findings are applied to the convenient and straightforward detection of single nucleotide polymorphisms (SNPs). When the target site in the sample DNA is completely complementary with the PNA, a notable amount of DNA/PNA duplex remains and thus the solution exhibits purple color. In the presence of even one mismatch between PNA and DNA, however, the DNA is completely digested by the enzyme and therefore the dye shows its intrinsic blue color. The SNPs in the apolipoprotein E gene of human DNA have been successfully genotyped by this method. 相似文献
995.
Salvino JM Gerard B Ye HF Sauvagnat B Dolle RE 《Journal of combinatorial chemistry》2003,5(3):260-266
An efficient solid-phase synthesis of mono-N-substituted piperazines is presented. The key transformation involves a selective borane amide bond reduction in the presence of a carbamate resin linkage. This synthetic route takes advantage of the large diverse pool of commercially available carboxylic acids, acid chlorides, and sulfonyl chlorides. The solid-phase approach facilitates parallel processing by eliminating the need for column chromatography after each synthetic step. The N-monosubstituted piperazines were shown to react with polymeric activated tetrafluorophenol (TFP) reagents to generate arrays of amides and sulfonamides in good purity for biological testing. 相似文献
996.
A simple and sensitive high-performance liquid chromatography method is developed for the simultaneous determination of (3,4-dihydroxyphenyl)-lactic acid (Dhpl) and protocatechuic aldehyde (Pal) in rat serum after oral administration of Radix Salviae miltiorrhizae extract. Serum samples are acidified with hydrochloric acid and extracted with ethyl acetate. Analysis of the extract is performed on a reversed-phase column and a mobile phase of 0.02% phosphoric acid-acetonitrile (91:9, v/v) with UV detection at 280 nm. Standard curves are linear in the range of 1.47-456.96 microg/mL for Dhpl and 0.124-7.936 microg/mL for Pal. For both regression coefficients, r(2) is greater than 0.993. Mean recovery is determined to be 75.23% and 84.06%, respectively, by analyzing serum standard containing 7.14, 57.12, and 228.48 microg/mL of Dhpl and 0.124, 0.992, and 3.968 microg/mL of Pal. The intraday precision (relative standard deviation) ranges from 3.91% to 12.03% at concentrations of 1.43, 57.12, and 228.48 microg/mL for Dhpl and 3.79% to 8.12% at concentrations of 0.124, 0.992, and 3.968 microg/mL for Pal. The interday precision (relative standard deviation) ranges from 5.06% to 9.93% for Dhpl and 3.05% to 10.00% for Pal, respectively, at the same three concentrations. This validated assay is applied to the determination of Dhpl and Pal concentrations and used to take a limited view of the pharmacokinetic profile in rat serum after oral administration of Radix Salviae miltiorrhizae extract. 相似文献
997.
基于WEB的虚拟系统为研究数字信号处理提供了一种新的方式,采用虚拟系统对数字信号的频谱分析及语音编码进行研究,通过ASP和ActiveX技术实现系统的动态交互和实时传输,初步实现了信号在网上的实时交互处理,该系统的研究成果已开始应用于教学,科研中。 相似文献
998.
夏业良 《杭州师范学院学报(社会科学版)》2001,(4):15-19
社区环境建设的滞后已直接成为制约社区生活质量提高的"瓶颈".如何在社区层面上构建一整套具有"人本化"特征和创新意义的制度安排,以适应居民迅速提高的对社区环境的进一步质量要求,将成为未来一个时期大都市社区建设的主要内容.从生态层面来获得对社区环境的再认识,是社区工作亟待加强的一个方面.社区生态可以看作是社区行为主体--居民与生活环境之间的互动现象,具体可分为基地环境、社区或邻里环境和住所环境三个生态层次. 相似文献
999.
Li Jin |chai Guo Huai |xi Lu Xian |feng Zhang Zhi |hong Ye Ming |sheng School of Physics Technology Wuhan University Wuhan Hubei China 《武汉大学学报:自然科学英文版》2003,8(3):821-824
0 IntroductionArtificialarthrosiseshavebeenwidelyusedintheoperatorsclinicalsurgeriesforthepatientswhosearthrosiseswerese riouslyseverelydamaged.Butmostofartificialarthrosisescanon lybeusedforabouttenyearslongduetotheseriousabrasion .Forthisreason ,theimprovementofthelongevityofartificialarthrosisbecomesanimportantsubjectofstudy .TheartificialarthrosisesbeingmadeupofTialloyTC4(Ti 6Al 4V)andthepolythenewithultrahighmolecularweighthavegreatpotentialitiesonim provinglongevitybecauseTC4canreac… 相似文献
1000.
For an energy-efficient induction machine, the life-cycle cost (LCC) usually is the most important index to the consumer. With this target, the optimization design of a motor is a complex nonlinear problem with constraints. To solve the problem, the authors introduce a united random algorithm. At first, the problem is divided into two parts, the optimal rotor slots and the optimization of other dimensions. Before optimizing the rotor slots with genetic algorithm ( GA), the second part is solved with TABU algorithm to simplify the problem. The numerical results showed that this method is better than the method using a traditional algorithm. 相似文献