全文获取类型
收费全文 | 6388篇 |
免费 | 210篇 |
国内免费 | 33篇 |
专业分类
化学 | 4962篇 |
晶体学 | 64篇 |
力学 | 83篇 |
数学 | 381篇 |
物理学 | 1141篇 |
出版年
2023年 | 24篇 |
2022年 | 49篇 |
2021年 | 62篇 |
2020年 | 74篇 |
2019年 | 104篇 |
2018年 | 61篇 |
2017年 | 50篇 |
2016年 | 115篇 |
2015年 | 105篇 |
2014年 | 154篇 |
2013年 | 313篇 |
2012年 | 362篇 |
2011年 | 427篇 |
2010年 | 225篇 |
2009年 | 259篇 |
2008年 | 440篇 |
2007年 | 413篇 |
2006年 | 448篇 |
2005年 | 398篇 |
2004年 | 374篇 |
2003年 | 307篇 |
2002年 | 314篇 |
2001年 | 119篇 |
2000年 | 81篇 |
1999年 | 70篇 |
1998年 | 79篇 |
1997年 | 79篇 |
1996年 | 81篇 |
1995年 | 65篇 |
1994年 | 46篇 |
1993年 | 55篇 |
1992年 | 43篇 |
1991年 | 49篇 |
1990年 | 26篇 |
1989年 | 27篇 |
1988年 | 35篇 |
1987年 | 41篇 |
1986年 | 61篇 |
1985年 | 69篇 |
1984年 | 56篇 |
1983年 | 37篇 |
1982年 | 60篇 |
1981年 | 59篇 |
1980年 | 52篇 |
1979年 | 51篇 |
1978年 | 39篇 |
1977年 | 34篇 |
1976年 | 33篇 |
1975年 | 25篇 |
1973年 | 29篇 |
排序方式: 共有6631条查询结果,搜索用时 15 毫秒
1.
Watanabe Sou Senzaki Tatsuya Shibata Atsuhiro Nomura Kazunori Takeuchi Masayuki Nakatani Kiyoharu Matsuura Haruaki Horiuchi Yusuke Arai Tsuyoshi 《Journal of Radioanalytical and Nuclear Chemistry》2019,322(3):1273-1277
Journal of Radioanalytical and Nuclear Chemistry - Extraction chromatography flow-sheet employing octyl(phenyl)-N,N-diisobutylcarbonoylmethylphosphine oxide and bis(2-ethylhexyl) hydrogen phosphate... 相似文献
2.
Minoru Koyama Dr. Takafumi Kawakami Dr. Takashi Okazoe Prof. Dr. Kyoko Nozaki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(46):10913-10917
Methacrylic esters, represented by methyl methacrylate (MMA), are widely used as commodity chemicals. Here, the one-pot synthesis of methacrylic esters from acetone, a haloform and alcohols in the presence of an organic base is described. Using DBU as the organic base for the reaction of acetone, chloroform and methanol in acetonitrile afforded MMA in 66 % yield. When the solvent was replaced by benzonitrile, the product MMA was successfully purified by distillation. Applicability of this process to various alcohols was also investigated to show ethyl, phenyl, CF3CH2, and n-C6F13CH2CH2 esters were obtained in moderate yields. The use of bromoform instead of chloroform resulted in the improvement of the yield, for example, methyl and n-C6F13CH2CH2 esters up to 81 and 70 %, respectively. The reaction with deuterated starting materials acetone-d6 and MeOH-d4, with DBU in acetonitrile afforded deuterated MMA (MMA-d8) in 70 % yield. 相似文献
3.
4.
Several investigations on the extraction of dioxins from soil and fly ash with supercritical fluid have been reported; however, few of them describe the influence of components on the extraction. We extracted dioxins from eight samples with different values of organic carbon content and surface area with supercritical CO(2) at a temperature of 463 K, a pressure of 40 MPa, and using 10% toluene as an entrainer. We researched the influence of the characteristics of soil and fly ash on supercritical CO(2) extraction of dioxins. The results revealed that the extraction efficiencies of PCDD/DFs and PCBs were high for all soil samples, while that of fly ash samples decreased with the increase in organic carbon content and surface area. The extraction efficiencies of dioxins from four standard samples, activated carbon, humic acid, alumina, and florisil, were also examined. The results revealed that the extraction efficiencies were strongly influenced by activated carbon like components present in the samples. 相似文献
5.
Behavior of fine crystalline particles of W5Si3 on a beta-Si3N4 substrate at high temperatures was observed by an in situ heating experiment in a transmission electron microscope. Some of the fine particles of W5Si3 moved in a to-and-fro manner. 相似文献
6.
Masashi Ohkawa Yuki Shirai Takeshi Goto Seishi Sekine Takashi Sato 《Fiber and Integrated Optics》2002,21(2):105-113
In this paper, a silicon-based integrated optic pressure sensor using an intermodal interference between the fundamental TM-like and TE-like modes is described. The sensor consists of a micromachined rectangular diaphragm and a straight polystyrene optical waveguide passing over the diaphragm. Its sensitivity is theoretically known to be strongly dependent on the position of the waveguide over the diaphragm. To experimentally investigate such dependence, we fabricated a sensor with a 1.2 mm ×10 mm ×20 μm diaphragm, over which waveguides were placed at 50 μm intervals. The measured phase sensitivity was 98 mrad/kPa for the waveguide nearest to the diaphragm edge. The measurement was also carried out for the other waveguides. As theoretically expected, the largest sensitivity was obtained for the waveguide nearest to the edge. 相似文献
7.
Summary In [6], we introduced and investigated the notions of strong β-I-open sets and strong β-I-continuous functions in ideal topological spaces. In this paper, we investigate further their important properties. 相似文献
8.
Akira Yanagisawa Prof. Dr. Takahiro Suzuki Takanori Koide Shogo Okitsu Takayoshi Arai Prof. Dr. 《化学:亚洲杂志》2008,3(10):1793-1800
A Barbier‐type regioselective propargylation of aldehydes and ketones with (3‐bromobut‐1‐ynyl)trimethylsilane has been achieved using reactive barium as a low‐valent metal in THF. Especially in the case of ketones, the corresponding homopropargylic alcohols form almost exclusively. In the reaction of α,β‐unsaturated carbonyl compounds, only 1,2‐adducts have been observed. This method is also applicable to propargylation of imines, and the corresponding homopropargylic amines are obtained regiospecifically in good yields with diastereomeric ratios of up to 87:13. 相似文献
9.
Yusong Wu Toshihiro Seo Shiro Maeda Takashi Sasaki Satoshi Irie Kensuke Sakurai 《Journal of Polymer Science.Polymer Physics》2004,42(22):4107-4115
Two benzoyl substituted chitosan derivatives, 3,6‐O‐dibenzoylchitosan (DBC) and 2‐N‐3,6‐O‐tribenzoylchitosan (TBC), were prepared, and their optical activities in organic solvent were investigated by circular dichroism (CD). For TBC, two splitting bands (a negative one at 288 nm and a positive one at 274 nm) corresponding to the 1Lb transition of the benzoyl group were observed in chloroform and dichloromethane, while only a negative CD band was recorded in N, N‐dimethylformamide (DMF). These results indicated that the transition moments of benzoyl groups were orderly arranged along the helical polymer chain when TBC was dissolved in a solvent with low polarity, but the same ordered structure did not appear in a polar solvent of DMF. For DBC, only negative CD signals corresponding to the 1Lb transition of the benzoyl group were observed, regardless of the solvent property, which indicated that the chromophores were not arranged in an ordered fashion with appropriate geometry to interact with one another to induce bi‐signate CD signals. Adding methanol or DMF to the solution of TBC/chloroform resulted in a progressive decrease of the intensity of the positive split band at 274 nm. The intensity of the positive band was weakened upon heating a solution of TBC/chloroform from 20 to 60 °C. The results suggested that the ordered arrangement of the chromophores in the TBC system was dependent on solvent and sensitive to temperature. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4107–4115, 2004 相似文献
10.
Oscillation is found in many biological systems, and among them the enzymatic oscillatory reaction has been well studied using an enzyme solution. We show in this study for the first time that oscillation occurs when catalase is immobilized to controlled pore glass (CPG). The oscillatory wave mode changes with the distance among the CPG, electrode, or dialysis membrane. The lower substrate concentration results in oscillation with a longer period. This tendency agrees with a previous study using an enzyme solution. Furthermore, we show that the oscillation occurs when no dialysis membrane is used. These results show the wider applicability of the system to analysis or novel device fabrication. 相似文献