全文获取类型
收费全文 | 18418篇 |
免费 | 2385篇 |
国内免费 | 1772篇 |
专业分类
化学 | 13012篇 |
晶体学 | 214篇 |
力学 | 1098篇 |
综合类 | 113篇 |
数学 | 1970篇 |
物理学 | 6168篇 |
出版年
2024年 | 74篇 |
2023年 | 377篇 |
2022年 | 617篇 |
2021年 | 697篇 |
2020年 | 699篇 |
2019年 | 704篇 |
2018年 | 587篇 |
2017年 | 582篇 |
2016年 | 828篇 |
2015年 | 794篇 |
2014年 | 948篇 |
2013年 | 1345篇 |
2012年 | 1576篇 |
2011年 | 1621篇 |
2010年 | 1138篇 |
2009年 | 1014篇 |
2008年 | 1252篇 |
2007年 | 1054篇 |
2006年 | 977篇 |
2005年 | 779篇 |
2004年 | 671篇 |
2003年 | 540篇 |
2002年 | 568篇 |
2001年 | 376篇 |
2000年 | 328篇 |
1999年 | 378篇 |
1998年 | 284篇 |
1997年 | 212篇 |
1996年 | 221篇 |
1995年 | 207篇 |
1994年 | 145篇 |
1993年 | 162篇 |
1992年 | 138篇 |
1991年 | 139篇 |
1990年 | 104篇 |
1989年 | 82篇 |
1988年 | 65篇 |
1987年 | 56篇 |
1986年 | 36篇 |
1985年 | 47篇 |
1984年 | 33篇 |
1983年 | 24篇 |
1982年 | 23篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1973年 | 6篇 |
1971年 | 6篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
借助定量金相、扫描电子显微镜、透射电子显微镜等微观分析手段对钨质量分数为93%的钨合金在15~50GPa冲击压力下微观结构响应性态进行了考察,发现了一些钨合金所特有的现象,即钨颗粒与粘结相交界处出现成分迁移,新相析出;并结合断口分析,探讨了钨合金在冲击作用下发生断裂的微观特征与韧脆转化间的关系及其物理本质。 相似文献
122.
Hongyu Liu Xinhui Guo Juncheng Chen Aobo Song Gu Jin Qizhi Yao Jiao Li Lingling Li 《大学化学》1986,35(12):221-226
This paper introduces an experiment about waste liquid recovery and effect evaluation in laboratory. Through this experiment, the basic operations of crystal preparation, chemical analysis and instrumental analysis are further consolidated. At the same time, it allows students to experience a series of possible problems of condition selection and control in the process of waste liquid treatment. We hope to improve the students' ability to analyze and solve problems, enhance their interest in learning, and strengthen their humanistic education. 相似文献
123.
A series of tetranuclear Mo(W)-Ag mixed-metal clusters have been synthesized by making use of the solid state reactions of [NH4]2[MYS3](M= Mo, W; Y= O, S), AgX(X= Cl, Br, I) and (n-Bu)4NX' (X' =Cl, Br), two of which [(n-Bu)4N]3[MoOS3Ag3Br4] (1) and [(n-Bu)4N]3[WS4Ag3Cl4] ( 2 ) have been structurally characterized by X-ray analysis. The crystal data: 1 , cubic, P4 3m, αequals;12.093(4) Å, Z=1, R =0.076; 2 , cubic, P4 3m, αequals;12.059(2) Å, Z =1, R =0.075. The cluster anion core [Ag3MS3X'] of the two compounds can be viewed as a cube in which the four metal atoms and the four non-metal atoms are statistically distributed, respectively. Substitution reaction with PPh3 ligand is also discussed for this type of tetranuclear clusters. 相似文献
124.
An easily prepared and highly efficient monodentate phosphoramidite ligand derived from BINOL, (S)-2,2'-O,O-(1,1'-binaphthyl)-dioxo-N,N-diethylphospholidine, was examined in the hydrogenation of both enamides and alpha-dehydroamino acid derivatives. The catalyst provided remarkably high enantioselectivities (up to 99.6% ee for enamides and >99.9% ee for alpha-dehydroamino acid derivatives). 相似文献
125.
Fluorescein has an extremely low luminescence intensity in acidic aqueous media. However, when it was bound to proteins, subsequent increase of luminescence intensity took place. Furthermore, when a hydrophobic tail, such as aliphatic hydrocarbons, was introduced to fluorescein, more dramatic increase of luminescence intensity was observed upon binding to proteins. In the present study, by utilizing this luminescence enhancement, three hydrophobic fluorescein dyes (5-dodecanoyl amino fluorescein, 5-hexadecanoyl amino fluorescein, and 5-octadecanoyl amino fluorescein) were examined as noncovalent fluorescent stains of protein bands in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Effective incorporation of the dyes to proteins in gels was accomplished either simply by adding dyes at the protein fixation step, or by treating gels with a staining solution after the fixation. The sensitivity of this staining method using the fluorescein derivatives was approximately 1 ng/band for most proteins. For some cases, protein bands containing as low as 0.1 ng were successfully visualized. In addition, the detection sensitivity showed much less protein-to-protein variation than silver staining. This new staining method was also successfully applied to two-dimensional electrophoresis of rat brain proteins. Its overall sensitivity was comparable to that of silver staining. 相似文献
126.
Jung-Ah Kang Ji-Sun Kwak Sang-Heon Park Kyu-Young Sim Seul Ki Kim Youngnim Shin In Jung Jung Jeong-In Yang Jang-Soo Chun Sung-Gyoo Park 《Experimental & molecular medicine》2021,53(4):560
Zinc is a trace element that is essential for immune responses. Therefore, changes in cellular zinc levels in specific immune cells may influence inflammatory autoimmune diseases, such as rheumatoid arthritis (RA). However, the regulation of zinc mobilization in immune cells and its role in the pathogenesis of RA are not fully understood. Thus, we investigated the roles of zinc transporters in RA pathogenesis. We demonstrated that ZIP8 was specifically upregulated in CD4+ T cells that infiltrated the inflamed joint and that ZIP8 deficiency in CD4+ T cells abrogated collagen-induced arthritis. ZIP8 deficiency dramatically affected zinc influx in effector T cells and profoundly reduced T cell receptor (TCR)-mediated signaling, including NF-κB and MAPK signaling, which are pathways that are involved in T helper (Th) 17 cell differentiation. Taken together, our findings suggest that ZIP8 depletion in CD4+ T cells attenuates TCR signaling due to insufficient cellular zinc, thereby reducing the function of effector CD4+ T cells, including Th17 cells. Our results also suggest that targeting ZIP8 may be a useful strategy to inhibit RA development and pathogenesis.Subject terms: Autoimmunity, Immunological disorders 相似文献
127.
Xin Sheng Li Yan Xin Chen Yao Jun Zhang Chun Xin Ji Qin Xin 《Reaction Kinetics and Catalysis Letters》1996,58(2):391-396
Hydrogen adsorption-desorption over Mo2N has been studied using a temperature-programmed technique. It is revealed that hydrogen on Mo2N exhibits very high mobility leading to migration of the surface hydrogen into the sublayer and bulk of the sample or the reverse. The surface hydrogen species are preferentially formed when adsorption is carried out below 573 K. On increasing the adsorption temperature to above 573 K, the quantity of hydrogen species located in the sublayer or/and bulk of the Mo2N sample increases significantly. 相似文献
128.
D. W. Kang G. P. Rajendran M. Zeldin 《Journal of polymer science. Part A, Polymer chemistry》1986,24(6):1085-1095
The thermal degradation of Me3SiO end-blocked polydimethylsiloxane (eb-PDMS) and polydimethylsiloxane-N-phenylsilazane (eb-PDMS–NPhSz) copolymer was studied. For both polymers relative degree of polymerization (DP /DP 0) as a function of conversion (1 – W/W0) data were obtained. For eb-PDMS the results were consistent with a mechanism involving a rate determining random siloxane bond cleavage initiation step followed by a rapid and complete depropagation of the active fragments evolving volatile cyclic oligomers. Rate constants (k) for initiation were obtained at four temperatures from plots of DP ?1 vs. time. An Arrhenius activation energy of approximately 80 kcal/mol was determined and is consistent with a SiOSi scission transition state. The degradation of eb-PDMS–NPhSz appears to follow the same depolymerization process evolving cyclic oligomers. Although DP /DP 0 vs. C data suggest a random cleavage–complete depolymerization mechanism, an Arrhenius plot suggests a more complex degradation mechanism. The role of impurities as degradation catalysts is discussed. 相似文献
129.
130.
A novel method for monitoring of mutagenic process of dimethyl sulfate to Salmonella typhimurium strain (TA100) was proposed by using piezoelectric quartz crystal impedance (PQCI) analysis technique. The time courses of responses piezoelectric impedance parameters for a quartz crystal in a culture system were simultaneously obtained and discussed. It was found that the motional resistance variation (DeltaR(m)) increases and frequency shift (Deltaf) of PQC sensor decreases correspondingly during the mutagenic process of the bacteria. These parameters could reflect the variations of viscosity and density of culture system. By fitting DeltaR(m) versus time curves toward Gompertz bacterial growth model, we obtained and discussed the bacterial growth parameters for both normal growth and mutagenic process. The experiments showed that the proposed method could provide real time and multidimensional impedance information to the monitoring of mutagenic process. 相似文献