全文获取类型
收费全文 | 3068篇 |
免费 | 115篇 |
国内免费 | 8篇 |
专业分类
化学 | 2479篇 |
晶体学 | 30篇 |
力学 | 49篇 |
数学 | 123篇 |
物理学 | 510篇 |
出版年
2022年 | 23篇 |
2021年 | 24篇 |
2020年 | 48篇 |
2019年 | 57篇 |
2018年 | 42篇 |
2017年 | 23篇 |
2016年 | 64篇 |
2015年 | 60篇 |
2014年 | 64篇 |
2013年 | 123篇 |
2012年 | 148篇 |
2011年 | 154篇 |
2010年 | 96篇 |
2009年 | 102篇 |
2008年 | 193篇 |
2007年 | 140篇 |
2006年 | 188篇 |
2005年 | 192篇 |
2004年 | 160篇 |
2003年 | 118篇 |
2002年 | 101篇 |
2001年 | 61篇 |
2000年 | 70篇 |
1999年 | 47篇 |
1998年 | 33篇 |
1997年 | 47篇 |
1996年 | 44篇 |
1995年 | 26篇 |
1994年 | 42篇 |
1993年 | 26篇 |
1992年 | 46篇 |
1991年 | 24篇 |
1990年 | 34篇 |
1989年 | 31篇 |
1988年 | 31篇 |
1987年 | 42篇 |
1986年 | 28篇 |
1985年 | 35篇 |
1984年 | 34篇 |
1983年 | 26篇 |
1982年 | 38篇 |
1981年 | 35篇 |
1980年 | 38篇 |
1979年 | 37篇 |
1978年 | 23篇 |
1977年 | 33篇 |
1976年 | 25篇 |
1975年 | 19篇 |
1974年 | 16篇 |
1973年 | 15篇 |
排序方式: 共有3191条查询结果,搜索用时 31 毫秒
21.
22.
Kozo Matsumoto Junichi Nakashita Hideki Matsuoka 《Journal of polymer science. Part A, Polymer chemistry》2006,44(15):4696-4707
Diblock copolymer poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane)‐block‐polystyrene (polyVSA‐b‐polySt) and triblock copolymer poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane)‐block‐polystyrene‐block‐poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane) (polyVSA‐b‐polySt‐b‐polyVSA), consisting of silazane and nonsilazane segments, were prepared by the living anionic polymerization of 1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane and styrene. PolyVSA‐b‐polySt formed micelles having a poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane) (polyVSA) core in N,N‐dimethylformamide, whereas polyVSA‐b‐polySt and polyVSA‐b‐polySt‐b‐polyVSA formed micelles having a polyVSA shell in n‐heptane. The micelles with a polyVSA core were core‐crosslinked by UV irradiation in the presence of diethoxyacetophenone as a photosensitizer, and the micelles with a polyVSA shell were shell‐crosslinked by UV irradiation in the presence of diethoxyacetophenone and 1,6‐hexanedithiol. These crosslinked micelles were pyrolyzed at 600 °C in N2 to give spherical ceramic particles. The pyrolysis process was examined by thermogravimetry and thermogravimetry/mass spectrometry. The morphologies of the particles were analyzed by atomic force microscopy and transmission electron microscopy. The chemical composition of the pyrolysis products was analyzed by X‐ray fluorescence spectroscopy and Raman scattering spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4696–4707, 2006 相似文献
23.
24.
LetX be ann-element set and letA and? be families of subsets ofX. We say thatA and? are crosst-intersecting if |A ∩ B| ≥ t holds for all A ∈A and for allB ∈ ?. Suppose thatA and ? are crosst-intersecting. This paper first proves a crosst-intersecting version of Harper's Theorem:
- There are two crosst-intersecting Hamming spheresA 0,? 0 with centerX such that |A| ≤ |A 0| and|?| ≤ |? 0| hold.
- Suppose thatt ≥ 2 and that the pair of integers (|A) is maximal with respect to direct product ordering among pairs of crosst-intersecting families. Then,A and? are Hamming spheres with centerX.
- Ifn + t = 2k ? 1 then |A| |?| ≤ max \(\left\{ {\left( {K_k^n + \left( {_{k - 1}^{n - 1} } \right)} \right)^2 ,K_k^n K_{k - 1}^n } \right\}\) holds, whereK l n is defined as \(\left( {_n^n } \right)\left( {_{n - 1}^n } \right) + \cdots + \left( {_l^n } \right).\)
- Ifn + t = 2k then |A| |? ≤ (K k n )2 holds.
25.
26.
Y Watanabe Y Matsumoto N Hori H Funato M Matsumoto 《Chemical & pharmaceutical bulletin》1991,39(11):3007-3012
The absorption of two kinds of insulin (from porcine or bovine pancreas) from the rectum of rabbits after the administration of hollow-type suppositories containing insulin and glyceryl-1-monooctanoate (GMO) as an absorption-enhancing agent was investigated. Two types of suppositories were employed: type I containing insulin in an aqueous solution (approx. 25 IU/mg/100 microliters citric buffer solution at pH 3.0) in the cavity of the suppository and GMO mixed with a base material (Witepsol H-15), and type II containing insulin in a crystalline form in the same amount as in type I. Without GMO, the insulin and glucose levels in plasma were unchanged, whereas a marked increase in the plasma levels of insulin and a decrease of glucose concentrations were found following coadministration of insulin and GMO by the type I suppository. Similar enhancement of rectal absorption of insulin was obtained from porcine and bovine sources. In the case of the crystalline insulin, despite the use of the same amount of GMO, porcine insulin was more efficiently absorbed than bovine insulin by the type II suppository. GMO enhances the absorption of insulin in an aqueous solution or a crystalline form, and the dissolution rate of insulin may be an important factor in the rectal absorption of insulin. 相似文献
27.
Takanori Suzuki Tomohiro Iwai Eisuke Ohta Hidetoshi Kawai Kenshu Fujiwara 《Tetrahedron letters》2007,48(20):3599-3603
Huge CD amplitude (A = +538) was attained by diastereomeric preference (50% de) for the title dication with two bis[4-(R)-sec-butoxyphenyl]methylium units in benzene at 23 °C. Intramolecular π-π stacking is the origin for effective transmission of point chirality to axial chirality to attain the chiroptical enhancement of 400-times. Thanks to the strong CD signaling, chiroptical changes upon electrolysis could be readily detected, thus realizing a new class of electrochiroptical response systems. Chiroptical properties could also be modified by solvent polarity. 相似文献
28.
Kazuhiko Matsumoto Tetsuya Tsuda Toshiyuki Nohira Rika Hagiwara Yasuhiko Ito Osamu Tamada 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(3):m186-m187
In the title complex, (C6H11N2)3[LaCl6], centrosymmetric octahedral hexachlorolanthanate anions are located at the corners and face‐centers of the monoclinic unit cell. The ring H atoms of the cations interact with the Cl atoms of the anions via hydrogen bonding, and bifurcation of the hydrogen bonding is observed. Cation–cation interactions via hydrogen bonding between the ring H atoms and π‐electrons of aromatic rings are also observed as in other imidazolium salts. 相似文献
29.
alpha-Tocopherol (alpha-Toc) was solubilized in aqueous solutions using 13 solubilizing agents and the products of oxidation by oxygen in the presence and the absence of Cu(II) were analyzed by HPLC. In the presence of Cu(II), the oxidation was accelerated and 5-formyl-7,8-dimethyltocol and alpha-tocoquinone were the major oxidation products. Their yields greatly increased in the presence of Cu(II). The yields and the rates of formation of the products were dependent on the properties of solubilizing agents and other conditions as well as the presence of Cu(II) or other metal ions. It is suggested that slight changes in the structure of the solubilizing agents affect the course of the reaction. 相似文献
30.