全文获取类型
收费全文 | 124211篇 |
免费 | 32274篇 |
国内免费 | 34202篇 |
专业分类
化学 | 79754篇 |
晶体学 | 3541篇 |
力学 | 8645篇 |
综合类 | 2314篇 |
数学 | 17962篇 |
物理学 | 78471篇 |
出版年
2024年 | 571篇 |
2023年 | 1127篇 |
2022年 | 2635篇 |
2021年 | 2435篇 |
2020年 | 2577篇 |
2019年 | 2930篇 |
2018年 | 2874篇 |
2017年 | 4436篇 |
2016年 | 3612篇 |
2015年 | 4695篇 |
2014年 | 5163篇 |
2013年 | 7466篇 |
2012年 | 8093篇 |
2011年 | 10005篇 |
2010年 | 13596篇 |
2009年 | 14160篇 |
2008年 | 8720篇 |
2007年 | 7475篇 |
2006年 | 7108篇 |
2005年 | 6822篇 |
2004年 | 6626篇 |
2003年 | 5108篇 |
2002年 | 4960篇 |
2001年 | 5221篇 |
2000年 | 4700篇 |
1999年 | 3752篇 |
1998年 | 2734篇 |
1997年 | 2395篇 |
1996年 | 2674篇 |
1995年 | 3099篇 |
1994年 | 3174篇 |
1993年 | 3233篇 |
1992年 | 2778篇 |
1991年 | 2349篇 |
1990年 | 1994篇 |
1989年 | 2100篇 |
1988年 | 2057篇 |
1987年 | 1304篇 |
1986年 | 1326篇 |
1985年 | 945篇 |
1984年 | 1065篇 |
1983年 | 463篇 |
1982年 | 978篇 |
1981年 | 813篇 |
1980年 | 819篇 |
1979年 | 591篇 |
1978年 | 553篇 |
1977年 | 641篇 |
1976年 | 1051篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
901.
Cheng Lu ZHANG Xiao Lei ZHU Ying Ge MA Li Wei ZOU 《中国化学快报》2006,17(2):163-164
12-Hydroxy-13-methylpodocarpa-9, 11, 13-trien-3-one 9 was isolated from the twigs ofCroton salutaris1. Many diterpenes exhibit significant bioactivities, such as antibac-terial and antitumour and 9 has a rare structure. In order to study the relationshipb… 相似文献
902.
Vytautas Getautis Albina Stanisauskaite Tadas Malinauskas Jolanta Stumbraite Valentas Gaidelis Vygintas Jankauskas 《Monatshefte für Chemie / Chemical Monthly》2006,23(12):1401-1409
Hydrazones containing 1-phenyl-1,2,3,4-tetrahydroquinoline units were synthesized starting from diphenylamine. These compounds
were found to constitute novel hole transporting materials and were characterized by the time of flight method. The hole drift
mobility in these compounds exceeds 10−6 cm2 V−1 s−1 at an electric field of 106 V cm−1. 相似文献
903.
Mousa Z. Al-Noaimi Raid J. Abdel-Jalil Mustafa M. El-Abadelah Salim F. Haddad Younis N. H. Baqi Wolfgang Voelter 《Monatshefte für Chemie / Chemical Monthly》2006,37(12):745-750
In the presence of RuCl3, N-phenylamidrazone underwent oxidative cyclization into 1,4-dihydro-1-phenyl-1,2,4-benzotriazine, the structure of which is
established by spectral and X-ray diffraction data. 相似文献
904.
Monika Schuster Robert Inführ Claudia Turecek Jürgen Stampfl Franz Varga Robert Liska 《Monatshefte für Chemie / Chemical Monthly》2006,4(4):843-853
To substitute cross-linked photopolymers in rapid prototyping of mold materials and therefore extend the range of materials
which can be casted, organo-soluble photopolymers were developed. Branched bisalkylacrylamides were suitable as base component
for such formulations, due to their high reactivity, good mechanical properties, and excellent solubility of the formed polymers.
These molding materials were used to prepare cellular biocompatible materials which could be used as bone replacement materials.
Biocompatible crosslinkers based on methacrylates from hydrolyzed gelatine or lactic acid ethyleneglycol blockcopolymers and
commercially available reactive diluents are the base components of such a formulation. Biocompatibility was investigated
by osteoblast-like cells. Cellular biocompatible parts were obtained by thermal polymerization in soluble mould materials
prepared by 3D-photoshaping. 相似文献
905.
Ivan Gutman Sabina Gojak Niko Radulovi? Boris Furtula 《Monatshefte für Chemie / Chemical Monthly》2006,46(2):277-284
In a recent work it was demonstrated that in linear hexagonal chains the distribution of π-electrons into rings (as computed
by means of the Randić–Balaban method) is uniform, irrespective of the nature of the terminal fragments. We now establish that an analogous, yet somewhat
more complex, uniformity in the π-electron distribution exists also in double linear hexagonal chains, as well as in some
other benzenoid systems. 相似文献
906.
Wafaa M. Abdou Neven A. Ganoub Amin F. Fahmy Abeer A. Shaddy 《Monatshefte für Chemie / Chemical Monthly》2006,46(10):105-116
Two simple and efficient one-pot procedures for the synthesis of a series of α-branched N-heterocycle-substituted methane-1,1-bisphosphonates
are outlined. In the first method, the parent halosubstrates were reacted with cyanomethylphosphonate followed by reaction
with dialkyl phosphonates to give asymmetrical or symmetrical bisphosphonates (BPs). In the second approach, the same halocompounds were reacted with tetraethyl methyl-1,1-bisphosphonate to give the requisite
BPs. Partial and complete hydrolysis of the prepared BPs were also investigated. The products contain functional groups advantageous for further synthetic modification as structural
units for coupling with the drug. 相似文献
907.
Mohamed Kameche Mohamed Feham 《International Journal of Infrared and Millimeter Waves》2006,27(5):687-705
Simple techniques for determining the broadband small signal equivalent circuit (SSEC) of MESFETs are presented in this paper.
The intrinsic elements are calculated using two-dimensional method from the Y parameters, which are obtained from the Fourier
analysis of the device transient response to voltage-step perturbations at the drain and gate electrodes. Whereas, the parasitic
external elements are determined by simple approximations used in transmission line modeling. In addition, a new technique
is also proposed to determine the source and drain series resistances. A comparison of the SSEC of three different MESFETs
technologies shows that the MESFETs on GaN and 4H-SiC are suitable for high power applications. The method used to determine
the intrinsic elements is validated with simulated data obtained by Monte Carlo method. 相似文献
908.
909.
以可溶性聚酰亚胺为反应底物,经氯甲基化反应制得氯甲基化聚酰亚胺,再以氯甲基为活性反应中心,在聚酰亚胺侧链上接枝聚丙二醇单丁醚(PPG),从而得到PPG侧链修饰聚酰亚胺.所制备的产物结构经红外光谱和核磁共振氢谱得以证实.介电常数及吸附脱附测试结果表明:经过大体积侧链PPG修饰后,聚合物的介电常数明显降低,由3.147降低至2.976;比体积和比表面积增大.同时,所制得的聚合物具有优良的溶解性能,在微电子工业中易于加工应用. 相似文献
910.