全文获取类型
收费全文 | 128489篇 |
免费 | 8791篇 |
国内免费 | 6003篇 |
专业分类
化学 | 60111篇 |
晶体学 | 1401篇 |
力学 | 9573篇 |
综合类 | 328篇 |
数学 | 37366篇 |
物理学 | 34504篇 |
出版年
2024年 | 182篇 |
2023年 | 1120篇 |
2022年 | 2076篇 |
2021年 | 2189篇 |
2020年 | 2271篇 |
2019年 | 2142篇 |
2018年 | 11832篇 |
2017年 | 11616篇 |
2016年 | 8422篇 |
2015年 | 3444篇 |
2014年 | 3375篇 |
2013年 | 4244篇 |
2012年 | 8483篇 |
2011年 | 14951篇 |
2010年 | 8761篇 |
2009年 | 8939篇 |
2008年 | 9718篇 |
2007年 | 11477篇 |
2006年 | 2847篇 |
2005年 | 3530篇 |
2004年 | 3219篇 |
2003年 | 3313篇 |
2002年 | 2256篇 |
2001年 | 1251篇 |
2000年 | 1179篇 |
1999年 | 1194篇 |
1998年 | 1044篇 |
1997年 | 947篇 |
1996年 | 988篇 |
1995年 | 840篇 |
1994年 | 686篇 |
1993年 | 611篇 |
1992年 | 482篇 |
1991年 | 453篇 |
1990年 | 380篇 |
1989年 | 298篇 |
1988年 | 236篇 |
1987年 | 220篇 |
1986年 | 216篇 |
1985年 | 185篇 |
1984年 | 129篇 |
1983年 | 129篇 |
1982年 | 96篇 |
1981年 | 77篇 |
1980年 | 75篇 |
1979年 | 62篇 |
1978年 | 42篇 |
1973年 | 41篇 |
1914年 | 45篇 |
1909年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
生物特异性功能高分子 总被引:1,自引:0,他引:1
模仿天然生物活性高分子关键作用点的化学组成,在高分子链上接上各种官能团或化学残基,制备具有与该天然高分子相似生物活性的高分子,即生物特异性功能高分子。本文主要介绍拟肝素高分子和似粘连 蛋白高分子两种生物特异性功能高分子。 相似文献
992.
993.
交联助剂对PPC/NBR弹性体结构和性能的影响 总被引:2,自引:1,他引:2
研究了马来酸酐(MA)及异氰脲酸三烯丙酯(TAIC)对聚丙撑碳酸酯/丁腈橡胶共混弹性体结构和性能的影响,发出加入MA或TAIC能有效地改善交联网络;加入适量MA能显著改善共混弹性体热氧老化稳定性;加入TAIC使共混弹性体具有优良的高弹特性和力学性能。 相似文献
994.
Xiaoling Bao Jianhong Liu Qingshu Zheng Wei Pei Yimei Yang Yanyun Dai Tao Tu 《中国化学快报》1990,30(12):2266-2270
A novel protocol allowing convenient and highly selective visual recognition of melamine in raw milk via selective metallo-hydrogel formation at a concentration as low as 10 ppm without any tedious pretreatment has been developed. 相似文献
995.
With the development of transgenic crops, regulations to label the genetically modified organisms (GMOs) and their derived products have been issued in many countries. Polymerase chain reaction (PCR) methods are thought to be reliable and useful techniques for qualitative and quantitative detection of GMOs. These methods are generally needed to amplify the transgene and compare the amplified results with that of a corresponding reference gene to get the reliable results. Specific primers were developed for the rapeseed (Brassica napus), high-mobility-group protein I/Y(HMG-I/Y) single-copy gene and PCR cycling conditions suitable for the use of this sequence as an endogenous reference gene in both qualitative and quantitative PCR assays. Both methods were assayed with 15 different rapeseed varieties, and identical amplified products were obtained with all of them. No amplification was observed when templates were the DNA samples from the other species of Brassica genus or other species, such as broccoli, stem mustard, cauliflower, Chinese cabbage, cabbage, sprouts, Arabidopsis thaliana, carrot, tobacco, soybean, mung bean, tomato, pepper, eggplant, plum, wheat, maize, barley, rice, lupine, and sunflower. This system was specific for rapeseed. Limits of detection and quantitation in qualitative and quantitative PCR systems were about 13 pg DNA (about 10 haploid genomes) and about 1.3 pg DNA (about 1 haploid genome), respectively. To further test the feasibility of this HMG-I/Y gene as an endogenous reference gene, samples containing transgenic rapeseed GT73 with the inserted glyphosate oxidoreductase (GOX) gene were quantitated. These demonstrated that the endogenous PCR detection systems were applicable to the qualitative and quantitative detection of transgenic rapeseed. 相似文献
996.
997.
Miniaturizing all dimensions of apparatus, such as electronics and computers, is the current trend followed by scientists
in various fields. The idea of Lab-on-a-Chip has significantly expanded and found its broad applications in analytical chemistry.
Microplasmas can act as a sample excitation source and are the miniaturized versions of full-sized plasmas. These can be created
in various forms, such as direct current, microwave induced, capacitively coupled and inductively coupled plasmas. Scaling
down the size would reduce the amount of gases, liquids and consumables required, as well as the sample analysis time, which
in turn would decrease the operating costs. Therefore, several research groups are involved in the development of microplasmas
for utilisation in analytical instruments. 相似文献
998.
999.
改进型甲醇合成催化剂NC208的催化特性 总被引:2,自引:0,他引:2
采用TPD、XRD、BET和H2S中毒试验等方法,对比研究三组份(Cu-Zn-Al)甲醇合成催化剂C207和添加少量金属氧化物的改进型催化剂NC208.结果表明,工作态NC208催化剂表面Cu+/Cu0的比值和价态稳定性大于C207. 相似文献
1000.
Guang-Ming Yang Peng Cheng Dai-Zheng Liao Zong-Hui Jiang Shi-Ping Yan Geng-Lin Wang Xin-Kan Yao Hong-Gen Wang 《Journal of Cluster Science》1998,9(4):465-471
The preparation, magnetic properties, and crystal structure of [(salen)Cu]4[(salen)Fe(H2O)2]2(ClO4)2 via hydrogen bonding are described [salen=N,N-ethylenebis (salicylideneiminate)]. Crystals are triclinic, of space group
, with cell constants a=12.853(3), b=13.921(3), c=14.251(3) Å, =68.68(3)°, =87.86(3)°, =86.82(3)°, and Z=1. The structure was solved and refined to R=0.064 and R=0.068. The structure comprises the hexanuclear units which result from the linking of four mononuclear fragments [(salen)Cu] and two mononuclear fragment [(salen)Fe(H2O)]+, through Cu -O H -O -Fe -O -H O -Cu hydrogen bonds of coordinating H2O. In this complex, FeIII ions are in almost square-planar surroundings. The temperature dependences of the magnetic susceptibilities of the complex have been studied in the 4.2–300 K range, indicating the presence of an antiferromagnetic interactions between metal ions. 相似文献