全文获取类型
收费全文 | 12846篇 |
免费 | 1166篇 |
国内免费 | 1200篇 |
专业分类
化学 | 4941篇 |
晶体学 | 84篇 |
力学 | 813篇 |
综合类 | 269篇 |
数学 | 6181篇 |
物理学 | 2924篇 |
出版年
2024年 | 28篇 |
2023年 | 145篇 |
2022年 | 233篇 |
2021年 | 298篇 |
2020年 | 367篇 |
2019年 | 364篇 |
2018年 | 331篇 |
2017年 | 417篇 |
2016年 | 507篇 |
2015年 | 359篇 |
2014年 | 593篇 |
2013年 | 1212篇 |
2012年 | 588篇 |
2011年 | 719篇 |
2010年 | 659篇 |
2009年 | 724篇 |
2008年 | 743篇 |
2007年 | 801篇 |
2006年 | 705篇 |
2005年 | 679篇 |
2004年 | 583篇 |
2003年 | 572篇 |
2002年 | 513篇 |
2001年 | 404篇 |
2000年 | 359篇 |
1999年 | 332篇 |
1998年 | 304篇 |
1997年 | 257篇 |
1996年 | 236篇 |
1995年 | 192篇 |
1994年 | 142篇 |
1993年 | 120篇 |
1992年 | 119篇 |
1991年 | 97篇 |
1990年 | 57篇 |
1989年 | 63篇 |
1988年 | 53篇 |
1987年 | 33篇 |
1986年 | 46篇 |
1985年 | 40篇 |
1984年 | 29篇 |
1983年 | 16篇 |
1982年 | 30篇 |
1981年 | 23篇 |
1980年 | 19篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 18篇 |
1976年 | 11篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
161.
We propose a method to locate saddle points that is based on the interplay between the driving coordinate and the restricted
quasi-Newton algorithm. The method locates the transition state using a reduced potential-energy surface. The reduced potential-energy
surface is characterized by the set of driving coordinates. The proposed algorithm starts at a point on the surface that is
slightly perturbed from either reactant or product and, in principle, converges to the transition state. Finally we give a
special type of update Hessian matrix formula that should be applied in optimizations carried out on reduced potential-energy
surfaces.
Received: 29 September 2000 / Accepted: 3 January 2001 / Published online: 3 April 2001 相似文献
162.
Efficient synthesis of cyclic -alkyl--dicarbonyl compounds of the cyclopentane, cyclohexane, tetronic acid, and -pyrone series from the corresponding cyclic -acyl--dicarbonyl compounds under the action of NaBH3(CN) in a THF--HCl system is described. 相似文献
163.
Dr. Dong Zhou Yi Chen Prof. Baohua Li Prof. Hongbo Fan Prof. Faliang Cheng Dr. Devaraj Shanmukaraj Prof. Teofilo Rojo Prof. Michel Armand Prof. Guoxiu Wang 《Angewandte Chemie (International ed. in English)》2018,57(32):10168-10172
Ambient‐temperature sodium–sulfur (Na–S) batteries are considered a promising energy storage system due to their high theoretical energy density and low costs. However, great challenges remain in achieving a high rechargeable capacity and long cycle life. Herein we report a stable quasi‐solid‐state Na‐S battery enabled by a poly(S‐pentaerythritol tetraacrylate (PETEA))‐based cathode and a (PETEA‐tris[2‐(acryloyloxy)ethyl] isocyanurate (THEICTA))‐based gel polymer electrolyte. The polymeric sulfur electrode strongly anchors sulfur through chemical binding and inhibits the shuttle effect. Meanwhile, the in situ formed polymer electrolyte with high ionic conductivity and enhanced safety successfully stabilizes the Na anode/electrolyte interface, and simultaneously immobilizes soluble Na polysulfides. The as‐developed quasi‐solid‐state Na‐S cells exhibit a high reversible capacity of 877 mA h g?1 at 0.1 C and an extended cycling stability. 相似文献
164.
《化学:亚洲杂志》2018,13(19):2770-2780
Owing to resource abundance, and hence, a reduction in cost, wider global distribution, environmental benignity, and sustainability, sodium‐based, rechargeable batteries are believed to be the most feasible and enthralling energy‐storage devices. Accordingly, they have recently attracted attention from both the scientific and industrial communities. However, to compete with and exceed dominating lithium‐ion technologies, breakthrough research is urgently needed. Among all non‐electrode components of the sodium‐based battery system, the electrolyte is considered to be the most critical element, and its tailored design and formulation is of top priority. The incorporation of a small dose of foreign molecules, called additives, brings vast, salient benefits to the electrolytes. Thus, this review presents progress in electrolyte additives for room‐temperature, sodium‐based, rechargeable batteries, by enlisting sodium‐ion, Na−O2/air, Na−S, and sodium‐intercalated cathode type‐based batteries. 相似文献
165.
《Journal of separation science》2018,41(13):2750-2758
An analytical method is presented for the determination of paraben preservatives in semisolid cream samples by matrix solid‐phase dispersion combined with supramolecular solvent‐based microextraction. Due to the oily and sticky nature of the sample matrix, parabens were first extracted from the samples by matrix solid‐phase dispersion using silica as sorbent material with a clean‐up performed with tetrahydrofuran in the elution step. The eluate (500 μL), 1‐decanol (120 μL), and water (4.4 mL) were then mixed in a polyethylene pipette to form supramolecular solvent. Finally, the analytes in the supramolecular solvent were separated and determined by liquid chromatography with ultraviolet detection. Under optimal extraction conditions, the extraction recoveries of the studied compounds were obtained in the range of 63–83%. The limits of detection for the analytes were between 0.03 and 0.04 μg/g. The precision of the method varied between 4.0–6.7 (intraday) and 6.2–7.9% (interday). Finally, the optimized procedure was applied to the determination of the target preservatives in a variety of cream samples (diaper rash, skin allergy, face and hand moisturizing) with satisfactory recoveries (86–102%). 相似文献
166.
《Macromolecular bioscience》2018,18(6)
Bone‐derived extracellular matrix (ECM) is widely used in studies on bone regeneration because of its ability to provide a microenvironment of native bone tissue. However, a hydrogel, which is a main type of ECM application, is limited to use for bone graft substitutes due to relative lack of mechanical properties. The present study aims to fabricate a scaffold for guiding effective bone regeneration. A polycaprolactone (PCL)/beta‐tricalcium phosphate (β‐TCP)/bone decellularized extracellular matrix (dECM) scaffold capable of providing physical and physiological environment are fabricated using 3D printing technology and decoration method. PCL/β‐TCP/bone dECM scaffolds exhibit excellent cell seeding efficiency, proliferation, and early and late osteogenic differentiation capacity in vitro. In addition, outstanding results of bone regeneration are observed in PCL/β‐TCP/bone dECM scaffold group in the rabbit calvarial defect model in vivo. These results indicate that PCL/β‐TCP/bone dECM scaffolds have an outstanding potential as bone graft substitutes for effective bone regeneration. 相似文献
167.
168.
169.
钠离子电池因地壳中丰富的钠资源以及金属钠与金属锂之间具有相似的物化性质等特点,成为后锂时代电池的候选者之一,然而较大的钠离子半径影响了其体系的动力学性能及离子迁移速率,因此寻找合适的电极材料成为其发展的关键.二硫化钒作为过渡金属硫属化合物,具有类石墨烯的层状结构,为钠离子的储存提供了足够的空间,同时其出色的导电性能也为其作为高性能钠离子电池的电极材料提供了保证.利用水热法与超声剥离法,可控制备出三种堆叠密度不同的铜钱状二硫化钒(VS2-Long、VS2-Middle、VS2-Short),并将其用于储钠性能研究.结果表明,堆叠程度最低的VS2-Short因其形貌结构特点而拥有较多的活性位点及较高结构稳定性,在100 mA·g-1的电流密度下,循环300圈后容量高达410 mAh·g-1;电流密度为2000 mA·g-1,可逆容量仍高达333 mAh·g-1.此外,还研究了二硫化钒作为钠离子电池电极材料的储能机制,通过非原位X射线粉末衍射(XRD)及透射电子显微镜(TEM)观测发现:放电过程中,电压在2.5~1.0 V发生嵌钠反应生成NaxVS2,之后逐渐开始转化反应生成Na2S和V;充电时Na2S和V转化生成NaxVS2,并最终脱钠生成VS2,即在0.2~2.5 V间VS2表现为嵌入转化的储钠机制. 相似文献
170.
Pedro Marcos Frugeri Camila Marchioni Ayla Campos do Lago Célio Wisniewski 《Analytical letters》2018,51(10):1492-1504
This work proposes a flow injection analysis system for sulfaguanidine determination in pharmaceutical and food samples. The method was based on the reaction of sulfaguanidine with nitronium ion to produce a colored complex whose absorbance was measured at 545?nm. The flow injection analysis system’s significant parameters were checked by a fractional factorial design 27–2 and optimization by a Doehlert matrix. The flow injection analysis system shows optimum values at 0.28, 2.00, and 0.11% (w/v) for N-naphtil ethylenediamine, ammonium sulfamate, and sodium nitrite concentrations, respectively. The possible interferents present in pharmaceutical and food samples were assessed by a multivariate technique and depicted on probability charts, indicating no significant interferences at the 95% level of confidence interval. The method showed detection and quantification limits of 0.012 and 0.039?mg?L?1, an analytical frequency of 30 readings h?1 and precision always lower than 5.0% expressed as the relative standard deviation. The obtained results were in accordance with those obtained by high-performance liquid chromatography. 相似文献