全文获取类型
收费全文 | 2428篇 |
免费 | 331篇 |
国内免费 | 343篇 |
专业分类
化学 | 1862篇 |
晶体学 | 40篇 |
力学 | 90篇 |
综合类 | 57篇 |
数学 | 382篇 |
物理学 | 671篇 |
出版年
2024年 | 3篇 |
2023年 | 45篇 |
2022年 | 58篇 |
2021年 | 94篇 |
2020年 | 95篇 |
2019年 | 117篇 |
2018年 | 98篇 |
2017年 | 105篇 |
2016年 | 130篇 |
2015年 | 135篇 |
2014年 | 150篇 |
2013年 | 232篇 |
2012年 | 194篇 |
2011年 | 230篇 |
2010年 | 163篇 |
2009年 | 148篇 |
2008年 | 163篇 |
2007年 | 141篇 |
2006年 | 113篇 |
2005年 | 111篇 |
2004年 | 82篇 |
2003年 | 54篇 |
2002年 | 50篇 |
2001年 | 33篇 |
2000年 | 40篇 |
1999年 | 38篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 24篇 |
1995年 | 28篇 |
1994年 | 13篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1974年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有3102条查询结果,搜索用时 312 毫秒
961.
Shou‐Li Wang Zhong Chen Xiao‐Jing Tong Yan‐Li Liu Xia Li Qiong‐Ming Xu Xiao‐Ran Li Shi‐Lin Yang 《Helvetica chimica acta》2013,96(6):1126-1133
Three new triterpenoids, 21β,22α‐diangeloyloxy‐3β,15α,16α,28‐tetrahydroxyolean‐12‐en‐23‐al ( 1 ), 21β‐angeloyloxy‐3β,15α,16α,28‐tetrahydroxy‐22α‐(2‐methylbutanoyloxy)olean‐12‐en‐23‐al ( 2 ), and 21β‐angeloyloxy‐3β,16α,28‐trihydroxy‐22α‐(2‐methylbutanoyloxy)olean‐12‐en‐23‐al ( 3 ), along with six known triterpenoids, were isolated from the roots of Camellia oleifera C.Abel . The structures of compounds 1 – 3 were elucidated on the basis of spectroscopic analyses. Moreover, all compounds isolated were evaluated for their cytotoxic activities by MTT (=3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl‐2H‐tetrazolium bromide) assay. 相似文献
962.
Zhenzhen Lu Shanli Yang Qiong Yang Shenglian Luo Chengbin Liu Yanhong Tang 《Mikrochimica acta》2013,180(7-8):555-562
We have modified a glassy carbon electrode by single-step electrodeposition of graphene (GR), gold nanoparticles (AgNPs), and chitosan (CS) directly from a solution containing graphene oxide, tetrachloroauric acid, and chitosan. The surface and electrochemical properties of the film-modified electrode were investigated by SEM and TEM images. The AuNPs have a diameter of about 20 nm and are uniformly dispersed in the matrix. Combining the advantages of GR (i.e., high surface area and conductivity), of AuNPs (excellent electrical conductivity) and CS (excellent film-forming ability and good water permeability), the hybrid film effectively enhances electron-transfer and promotes the response to lead(II) ion. Under the optimum conditions, a linear relationship exists between electrical current and the concentration of lead (II) ion in the range between 0.5 to 100 μg?L-1, with a detection limit of 1 ng?L-1 (at an SNR of 3). The electrode was successfully applied to the detection of lead(II) in spiked samples of river water. Figure
Graphene–Au nanoparticles–chitosan (GR–AuNPs–CS) was fabricated by one-step electrodeposition. The obtained GR–AuNPs–CS hybrid was used for trace analysis of the lead (II). 相似文献
963.
Qiong‐Yan Wang 《Mathematical Methods in the Applied Sciences》2019,42(9):3044-3053
By using Nevanlinna theory, we generalize a result given by Wittich to complex differential‐difference equations. The result obtained is that the differential‐difference equation in f which is of only one dominant term, has no admissible meromorphic solution f with hyper‐order less than 1 provided N(r,f) = S(r,f). 相似文献
964.
本文利用常微分方程的连续有限元法计算了A2B模型的分子的经典轨迹和能量误差,将计算延长到10^-sS,并与辛算法进行了比较.结果表明,在微观反映动力学研究所考虑的时间范围内,有限元法的结果与理论分析一致,能较长时间保持能量守恒和系统整体结构,并在数值计算上探讨了守恒性和近似程度,结果与理论相吻合。 相似文献
965.
用化学气相沉积法在石英基底上制备了阵列式碳纳米管膜,并且把这层薄膜转移到纸质胶带上,用透射电子显微镜观察了膜的结构.初步研究了纸质基底阵列式碳纳米管膜对含铅离子溶液、铬溶液中的铅离子、铬离子的过滤特性.研究表明:碳纳米管膜可以过滤溶液中的绝大部分的重金属离子. 相似文献
966.
0–1 problems are often difficult to solve. Although special purpose algorithms (exact as well as heuristic) exist for solving
particular problem classes or problem instances, there are few general purpose algorithms for solving practical-sized instances
of 0–1 problems. This paper deals with a general purpose heuristic algorithm for 0–1 problems. In this paper, we compare two
methods based on simulated annealing for solving general 0–1 integer programming problems. The two methods differe in the
scheme used for neighbourhood transitions in the simulated annealing framework. We compare the performance of the two methods
on the set partitioning problem. 相似文献
967.
968.
甘蓝型油菜新型恢复系Nsa恢1及其后代的GISH分析 总被引:2,自引:0,他引:2
用基因组原位杂交(genomic in situ hybridization,GISH)结合双色荧光原位杂交(double-colour fluorescence in situ hybridization,dc-FISH)技术,对甘蓝型油菜新型恢复系Nsa恢1及其后代进行了研究,结果表明,Nsa恢1为甘蓝型油菜-新疆野生油菜二体异附加系,包含了甘蓝型油菜全基因组和新疆野生油菜1对染色体,这1对新疆野生油菜染色体为同源染色体.不育系分别与保持系、恢复系Nsa恢1、保持系杂交后获得了BC3代不育株及可育株,GISH-dcFISH分析结果表明,BC3代可育株为甘蓝型油菜-新疆野生油菜单体异附加系,而不育株中不含新疆野生油菜染色体.说明恢复基因位于Nsa恢1的新疆野生油菜染色体上,为下一步克隆这一新型恢复基因提供了依据. 相似文献
969.
氯化钙在10X分子筛上的微波强化分散及其氨吸附的研究 总被引:3,自引:0,他引:3
利用干混法将氯化钙担载于10X分子筛上,通过微波法强化分散,研究了不同条件下样品的XRD图和氨吸附量,并与同样氯化钙担载量的焙烧法样品进行了比较.结果表明,微波法能显著提高CaCl2的分散度,且对应样品的氨吸附量显著提高.CaCl2在10X分子筛上的单层分散阈值在0.4 g/g~0.5 g/g之间,担载量为0.5 g/g的样品的氨吸附量最大,在35℃时达到0.575 g/g.在85 ℃时样品的吸附量都很小,这对利用低温余热脱附很有利.样品的适宜微波处理时间在10 min~20 min之间.同时,利用比表面分析和红外光谱分析证明微波法可以强化分散且不改变分子筛结构. 相似文献
970.
F. Guillot B. Amstatt E. Bellet-Amalric E. Monroy L. Nevou L. Doyennette F.H. Julien Le Si Dang 《Superlattices and Microstructures》2006,40(4-6):306
We present a study of the effect of Si doping localization on the optical and structural properties of GaN/AlN multiple-quantum-well structures for intersubband (ISB) absorption at 1.55 μm. Samples were either undoped or Si doped in different regions (barrier, quantum well (QW), middle of barrier or middle of QW). Structural characterization by atomic force microscopy and X-ray diffraction does not show significant differences in the crystalline quality. All doped samples present room-temperature p-polarized ISB absorption of about 1%–2% per pass, with a line width of 80–90 meV. In contrast, undoped samples present a weaker ISB absorption with a record line width of 40 meV. Both photoluminescence (PL) and ISB absorption display structured shapes whose main peaks correspond to monolayer fluctuations of the well thickness. The emission and absorption line widths depend on the Si doping concentration, but not on the Si location. 相似文献