全文获取类型
收费全文 | 79847篇 |
免费 | 12091篇 |
国内免费 | 8758篇 |
专业分类
化学 | 42568篇 |
晶体学 | 727篇 |
力学 | 3562篇 |
综合类 | 430篇 |
数学 | 6896篇 |
物理学 | 22479篇 |
无线电 | 24034篇 |
出版年
2024年 | 347篇 |
2023年 | 2032篇 |
2022年 | 2781篇 |
2021年 | 3413篇 |
2020年 | 3289篇 |
2019年 | 2979篇 |
2018年 | 2576篇 |
2017年 | 2637篇 |
2016年 | 3504篇 |
2015年 | 3863篇 |
2014年 | 4575篇 |
2013年 | 5724篇 |
2012年 | 6793篇 |
2011年 | 6763篇 |
2010年 | 4984篇 |
2009年 | 4892篇 |
2008年 | 5225篇 |
2007年 | 4544篇 |
2006年 | 4176篇 |
2005年 | 3649篇 |
2004年 | 2702篇 |
2003年 | 2203篇 |
2002年 | 2017篇 |
2001年 | 1676篇 |
2000年 | 1482篇 |
1999年 | 1707篇 |
1998年 | 1386篇 |
1997年 | 1260篇 |
1996年 | 1238篇 |
1995年 | 1088篇 |
1994年 | 933篇 |
1993年 | 794篇 |
1992年 | 683篇 |
1991年 | 580篇 |
1990年 | 446篇 |
1989年 | 332篇 |
1988年 | 251篇 |
1987年 | 214篇 |
1986年 | 198篇 |
1985年 | 177篇 |
1984年 | 111篇 |
1983年 | 105篇 |
1982年 | 67篇 |
1981年 | 50篇 |
1980年 | 31篇 |
1979年 | 19篇 |
1977年 | 21篇 |
1976年 | 21篇 |
1975年 | 24篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
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
992.
用AM1方法计算了马来酸酐、羟基自由基及其加成产物α-羟基丁二酸酐基自由基的电子结构、电荷分布和键级.应用前线轨道理论和成键三原则研究了羟基自由基引发下马来酸酐聚合过程中α-羟基丁二酸酐基自由基活性中间体参与反应的可能性及其自由基聚合反应机理.计算结果表明:马来酸酐基态分子的HOMO和LUMO分别对应于双键CC的成键π-MO和反键π -MO;马来酸酐的羟基自由基加成反应活化能计算值为55 7kJ/mol;马来酸酐在羟基自由基引发下的自由基聚合产物是链式结构,与实验事实相符. 相似文献
993.
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
994.
995.
996.
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
997.
在25±0.02℃、0.025mol·dm~(-3)KCl介质及磷酸盐缓冲条件下,用光度滴定法研究了羟基-氧钼(V)[5,10,15,20-四(4-磺酸基苯基)]卟啉配合物在水溶液中的二聚平衡,用线性最小平方法确定了平衡模型,求得二聚反应平衡常数pK_el=4.34±0.28,单体的摩尔吸收εm(447um)=1.27×10~4εm(475um)=2.01×10~4;二聚体的摩尔吸收ε_d(447nm)=3.17×10~4,ε_d(475nm)=1.40×10~4。 相似文献
998.
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
999.
1000.