全文获取类型
收费全文 | 16260篇 |
免费 | 2821篇 |
国内免费 | 1933篇 |
专业分类
化学 | 11693篇 |
晶体学 | 174篇 |
力学 | 1166篇 |
综合类 | 69篇 |
数学 | 1724篇 |
物理学 | 6188篇 |
出版年
2024年 | 38篇 |
2023年 | 342篇 |
2022年 | 506篇 |
2021年 | 559篇 |
2020年 | 647篇 |
2019年 | 607篇 |
2018年 | 540篇 |
2017年 | 498篇 |
2016年 | 852篇 |
2015年 | 744篇 |
2014年 | 952篇 |
2013年 | 1157篇 |
2012年 | 1519篇 |
2011年 | 1501篇 |
2010年 | 1023篇 |
2009年 | 951篇 |
2008年 | 1096篇 |
2007年 | 978篇 |
2006年 | 885篇 |
2005年 | 788篇 |
2004年 | 552篇 |
2003年 | 448篇 |
2002年 | 435篇 |
2001年 | 361篇 |
2000年 | 318篇 |
1999年 | 352篇 |
1998年 | 277篇 |
1997年 | 248篇 |
1996年 | 293篇 |
1995年 | 278篇 |
1994年 | 195篇 |
1993年 | 162篇 |
1992年 | 159篇 |
1991年 | 151篇 |
1990年 | 133篇 |
1989年 | 105篇 |
1988年 | 91篇 |
1987年 | 73篇 |
1986年 | 52篇 |
1985年 | 42篇 |
1984年 | 31篇 |
1983年 | 27篇 |
1982年 | 14篇 |
1981年 | 16篇 |
1980年 | 9篇 |
1978年 | 2篇 |
1972年 | 1篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
972.
973.
A new strategy for the generation of the active Pd-alkyl species from aminal via C-N bond activation has been established,in which the formation of zwitterionic... 相似文献
974.
975.
以壳聚糖为基材,分别以氯磺酸、三甲胺.三氧化硫和丙磺酸内酯为磺化试剂,制备了3,6-O-磺化壳聚糖(OCS)、2-N-磺化壳聚糖(NCS)和2-N-磺丙基壳聚糖(PCS)3种磺化壳聚糖.采用红外光谱、核磁共振谱证明了磺化壳聚糖的结构,元素分析测定了磺化壳聚糖的磺化率.以组织修复过程中一种重要的活性因子——碱性成纤维细胞生长因子(bFGF)为目标因子,通过体外成纤维细胞培养实验,评价了不同磺化壳聚糖对bFGF活性的保护能力.结果显示,相对于未改性壳聚糖(CS),磺化壳聚糖对成纤维细胞的形态无显著影响.细胞活性检测结果显示,OCS和PCS对bFGF活性无明显的保护能力;NCS能有效提高bFGF促进成纤维细胞活性的能力,其对bFGF活性的保护能力可达肝素70%左右.磺化壳聚糖的bFGF活性保护能力不随磺化率的改变而变化. 相似文献
976.
977.
Triple-negative breast cancer (TNBC) is considered to be aggressive based on its low overall survival and disease-free rates. Currently, there is no molecular-targeted therapy. The identification of a suitable biomarker is still a research focus for TNBC at the present time. Amino acid metabolism fulfills multiple important physiological roles in humans. Their metabolic abnormalities have been reported in numerous cancer studies and amino acid pathways may also be chemotherapeutic targets. This study reports the profiling analysis of amino acids in TNBC and non-TNBC cell lines for detecting biomarkers based on the strategy of N-phosphorylation labeling with liquid chromatography–tandem mass spectrometry (LC–MS). Glutamine (Gln) was found to be significantly down-regulated in TNBC cells because it was largely absorbed and consumed in the TNBC cell lines. These results indicate faster proliferation of TNBC and higher consumption of glutamine to meet the material and energy demand, suggesting its potential role in TNBC progression. Hence, glutamine may be regarded as a biomarker and Gln-targeted approaches may become a new therapeutic strategies for TNBC. 相似文献
978.
Xiaolan Tong Shan Wang Jun Zuo Yingchong Ge Qiang Gao Suijun Liu Jianhua Ding Fen Liu Jianqiang Luo Jianbo Xiong 《中国化学快报》2021,32(2):604-608
Two new hydrostable two-dimensional(2 D) uranyl coordination complexes [(UO_2)_5(μ_3-O)_2(nbca)_2].7 H_2O(1) and [(UO_2)_3(nbca)_2(H_2O)_3]·2 H_2O(2)(H_3 nbca=5-nitro-1,2,3-benzenetricarboxylic acid) were hydrothermal synthesized.Single-crystal structural refinements reveal that both of the two complexes were formed by the packing of 2D uranyl coordination sheets via the hydrogen bonds.The nbca ligand coordinating to the uranyl polyhedron centers constructed the 2D sheets.There are UO_8 hexagonal bipyramids and UO_7 pentagonal bipyramids in 1 while only U07 pentagonal bipyramids in 2.Photocatalytic degradation of rhodamine B(RhB) in aqueous solution was studied.Complex 2 possesses better performance than 1 with 96.2 % of the RhB was degraded in only 60 min.Mechanism studies reveal that the dissolved oxygens are essential to the RhB degradation.The photocurrent density of 2 is more stable than that of 1,which indicating the stronger ability to separate photoexcited electrons and hole pairs of 2. 相似文献
979.
This paper uses heat transfer experiments and computational fluid dynamics (CFD) simulations to investigate the conjugate heat transfer (CHT) in a high-pressure pneumatic control valve assembly. A heat transfer test rig was constructed, and time–temperature histories of five test points placed on the valve assembly’s outer surface were recorded for study validation. The Unsteady Reynolds-Averaged Navier–Stokes (URANS) CFD methods with the standard k-ε turbulence closure equations were adopted in the numerical computations. Polyhedral grids were used; time step and mesh convergence studies were conducted. Simulated and measured temperatures profile comparisons revealed a good agreement. The CHT results obtained from CFD showed huge velocity fields downstream of the valve throat and the vent hole. The airflow through the valve was icy, mainly in the supersonic flow areas. Low temperatures below 273.15 K were recorded on the internal and external walls of the valve assembly. The consistency of the measured data with the numerical results demonstrates the effectiveness of polyhedral grids in exploring the CHT using CFD methods. The local entropy production rate analysis revealed that irreversibility is mainly due to viscous dissipation. The current CHT investigation provides a potential basis for thermostress analysis and optimization. 相似文献
980.
Liu-Qiao Zhang Yang Gao Zhi-Hao Huang Wei Zhang Nian-Chen Zhou Zheng-Biao Zhang Xiu-Lin Zhu 《高分子科学》2021,39(1):60-69
The controlled and efficient synthesis of polymers with tailored topologies is challenging but important for exploring structure/property research. Herein, we proposed a concept of macro-latent monomer to achieve the controlled growth of polymer topologies.The macro-latent monomer was installed by a dynamic furan/maleimide covalent bond at the chain terminal. One-shot reversible additionfragmentation chain transfer(RAFT) polymerization of styrene and the macro-latent monomer created controlled growth of polymer topologies.Low temperature such as 40 ℃ could not activate the macro-latent monomer and thus the polymerization created the homo-polystyrene. By contrast, high temperature of ~110 ℃ activated the macro-latent monomer, and a maleimide-terminated macro-monomer was released via the retro-Diels Alder reaction. This macro-monomer immediately joined the cross polymerization with styrene and thus produced the side chains. By delicately manipulating the polymerization temperature, the predetermined placement of the macro-latent monomer-derived polymeric sidechains created controllably growing topologies, including star-, π-shaped, and density-variable grafting copolymers. This work paved a new way for creating on-demand topologies and would greatly enrich the topology synthesis. 相似文献