全文获取类型
收费全文 | 13750篇 |
免费 | 2173篇 |
国内免费 | 1130篇 |
学科分类
数理化 | 17053篇 |
出版年
2024年 | 38篇 |
2023年 | 179篇 |
2022年 | 540篇 |
2021年 | 550篇 |
2020年 | 492篇 |
2019年 | 439篇 |
2018年 | 356篇 |
2017年 | 581篇 |
2016年 | 619篇 |
2015年 | 685篇 |
2014年 | 933篇 |
2013年 | 995篇 |
2012年 | 945篇 |
2011年 | 895篇 |
2010年 | 813篇 |
2009年 | 893篇 |
2008年 | 816篇 |
2007年 | 854篇 |
2006年 | 740篇 |
2005年 | 689篇 |
2004年 | 631篇 |
2003年 | 490篇 |
2002年 | 350篇 |
2001年 | 309篇 |
2000年 | 289篇 |
1999年 | 269篇 |
1998年 | 199篇 |
1997年 | 216篇 |
1996年 | 216篇 |
1995年 | 164篇 |
1994年 | 97篇 |
1993年 | 104篇 |
1992年 | 97篇 |
1991年 | 77篇 |
1990年 | 68篇 |
1989年 | 67篇 |
1988年 | 69篇 |
1987年 | 60篇 |
1986年 | 37篇 |
1985年 | 45篇 |
1984年 | 27篇 |
1983年 | 24篇 |
1982年 | 34篇 |
1981年 | 21篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1973年 | 4篇 |
1971年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Cosmic dust and our origins 总被引:1,自引:0,他引:1
J Mayo Greenberg 《Surface science》2002,500(1-3):793-822
The small solid particles in the space between the stars provide the surfaces for the production of many simple and complex molecules. Processes involving the effects of ultraviolet irradiation of the thin (hundredth micron) mantles are shown to produce a wide range of molecules and ions also seen in comets. Some of the more complex ones inferred from laboratory experiments are expected to play an important role in the origin of life. An outline of the chemical evolution of interstellar dust as observed and as studied in the laboratory is presented. Observations of comets are shown to provide substantial evidence for their being fluffy aggregates of interstellar dust as it was in the protosolar nebula, i.e. the interstellar cloud which collapsed to form the solar system. The theory that comets may have brought the progenitors of life to the earth is summarized. 相似文献
2.
Donghyun Cho Taihyun Chang Apostolos Avgeropoulos Nikos Hadjichristidis 《European Polymer Journal》2003,39(11):2155-2160
Temperature gradient interaction chromatography (TGIC) was applied for the separation of a complex miktoarm star copolymer which has one polystyrene (PS) arm and three polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer arms. Such miktoarm star polymers are much more difficult to characterize than branched homopolymers since the byproduct, typically polymers with missing arm(s) or coupled products, have not only different molecular weights but also different compositions. TGIC was able to fully separate the byproducts, and the composition of the molecular species corresponding to the different separated elution peaks was determined by two methods, fractionation/NMR and multiple detection (UV and RI). A reasonable agreement between the results of the two methods was obtained. By using the composition found, the corresponding molecular weights were determined by multi-angle light scattering detection. Based on the composition and the molecular weight we were able to identify the structure of the different molecular species. 相似文献
3.
Volodymyr Malyutenko Vitalii Borblik Victor Vainberg 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):563
An all-optical approach to convert terahertz radiation (THz, wavelength λ1) into infrared (IR, peak wavelength λ2) is presented. We show that this up-conversion process is due to the photon drag effect induced by the THz radiation in intrinsic narrow-gap semiconductors followed by spatial redistribution of current carriers and band-to-band radiative recombination. The process results in non-selective high-speed (ns range rise/fall times) IR imaging of positive (conventional luminescence) and/or negative (negative luminescence) contrasts. Estimates made for an InSb pixelless converter at 300 K and moderate THz intensity (kW/cm2) show that this up-conversion process (with λ1/λ2>102) can be observed with a conventional thermal imaging camera. 相似文献
4.
5.
L. K. Seah U. S. Dinish S. K. Ong Z. X. Chao V. M. Murukeshan 《Optics & Laser Technology》2004,36(5):371-376
Imaging of latent fingerprints using time-resolved (TR) method offers a broader platform to eliminate the unwanted background emission. In this paper, a novel TR imaging technique is demonstrated and implemented, which facilitates the detection of latent fingerprints with nanosecond resolution. Simulated experiments were carried out with two overlapping fingerprints treated with two fluorescent powders having different lifetimes in nanosecond range. The dependence of the fluorescence emission intensity in nanosecond resolution of TR imaging is also revealed. 相似文献
6.
7.
采用表面光滑玻璃珠作为载体材料,用1:40的腹泻性大肠杆菌诊断血清进行包被。可制成免疫珠。这种免疫珠能与腹泻性大肠杆菌发生特异性结合。经乳糖蛋白胨培养液培养,然后根据其产酸产气进行判断。能在18h内完成腹泻性大肠杆菌的检测。其灵敏度为样液中含有腹泻性大肠杆菌数必须大于10CFu/mL.该法简单、快速、易操作、灵敏度高。 相似文献
8.
Capillary gas chromatography coupled to microwave-inducedplasma detection furnishes sensitivity adequate for trace analysis when the signal is monitored at a carbon emission line. Work performed with one of these systems at high electronic gain for the carbon signal has revealed solvent band widths in excess of four minutes; these impeded quantification of peaks eluting after the solvent. This report discusses two phenomena which could be related to the unexpected intensity of this solvent response: photomultiplier tube saturation and carbon deposits in the quartz plasma discharge tube. 相似文献
9.
10.