全文获取类型
收费全文 | 2399篇 |
免费 | 51篇 |
国内免费 | 10篇 |
专业分类
化学 | 1229篇 |
晶体学 | 46篇 |
力学 | 50篇 |
数学 | 321篇 |
物理学 | 814篇 |
出版年
2022年 | 19篇 |
2021年 | 25篇 |
2020年 | 34篇 |
2019年 | 39篇 |
2018年 | 49篇 |
2017年 | 51篇 |
2016年 | 63篇 |
2015年 | 45篇 |
2014年 | 86篇 |
2013年 | 173篇 |
2012年 | 116篇 |
2011年 | 128篇 |
2010年 | 96篇 |
2009年 | 94篇 |
2008年 | 105篇 |
2007年 | 81篇 |
2006年 | 65篇 |
2005年 | 63篇 |
2004年 | 52篇 |
2003年 | 48篇 |
2002年 | 44篇 |
2001年 | 23篇 |
2000年 | 27篇 |
1999年 | 21篇 |
1998年 | 20篇 |
1997年 | 16篇 |
1996年 | 20篇 |
1995年 | 19篇 |
1994年 | 19篇 |
1993年 | 35篇 |
1992年 | 31篇 |
1990年 | 19篇 |
1989年 | 28篇 |
1988年 | 31篇 |
1987年 | 25篇 |
1986年 | 26篇 |
1985年 | 29篇 |
1984年 | 29篇 |
1983年 | 26篇 |
1982年 | 31篇 |
1981年 | 43篇 |
1980年 | 46篇 |
1979年 | 32篇 |
1978年 | 42篇 |
1977年 | 43篇 |
1976年 | 27篇 |
1975年 | 26篇 |
1974年 | 26篇 |
1973年 | 38篇 |
1972年 | 24篇 |
排序方式: 共有2460条查询结果,搜索用时 15 毫秒
111.
Induced twisted-grain-boundary phases in the binary mixtures of a cholesteric and a nematic compound
Thermodynamical, optical-texture and dielectric studies have been performed to study the phase diagram of the binary system of 5-cholesten-3β-ol-octanoate and 4-n-nonyloxybenzoic acid. It is observed that low concentrations of 5-cholesten-3β-ol-octanoate (2–30?mol?%) in 4-n-nonyloxybenzoic acid induce a mean-field phase diagram derived by Renn within the framework of the chiral Chen–Lubenski model. Various optical textures of the twisted-grain-boundary (TGB) phases under different conditions of molecular anchoring have been observed. Weak transitions related to the TGB phases have been detected by temperature dependent dielectric spectroscopy. 相似文献
112.
Dhamaniya Bhanu Pratap Kumar Ashavani Srivastava A. K. Tawale J. S. 《Research on Chemical Intermediates》2017,43(1):387-399
Research on Chemical Intermediates - N and F codoped nanophotocatalysts were synthesized by sol–gel method and their photocatalytic activity were studied for the degradation of insecticide... 相似文献
113.
Malik Abdul Waseem ShireenAnjali Srivastava Arjita SrivastavaRahila I.R. Siddiqui 《Tetrahedron letters》2014
Reusable [bmIm]OH was found to be a highly efficient renewable homogenous catalyst for the rapid and convenient synthesis of benzoxazine-4-one derivatives from o-iodobenzoic-acid and benzonitrile at 75 °C in moderate to good yields. This methodology provides a facile and straightforward path to construct other related heterocycles in an eco-compatible fashion. 相似文献
114.
Xiao-Jun Yang H.M. Srivastava Ji-Huan He Dumitru Baleanu 《Physics letters. A》2013,377(28-30):1696-1700
In this Letter, we propose to use the Cantor-type cylindrical-coordinate method in order to investigate a family of local fractional differential operators on Cantor sets. Some testing examples are given to illustrate the capability of the proposed method for the heat-conduction equation on a Cantor set and the damped wave equation in fractal strings. It is seen to be a powerful tool to convert differential equations on Cantor sets from Cantorian-coordinate systems to Cantor-type cylindrical-coordinate systems. 相似文献
115.
H. M. Srivastava Shy-Der Lin Shuoh-Jung Liu Han-Chun Lu 《Russian Journal of Mathematical Physics》2012,19(1):121-130
Motivated essentially by their potential for applications in the mathematical, physical, and statistical sciences, the object
of this paper is to investigate several general families of hypergeometric polynomials and their associated multiple integral
representations. By suitably specializing the main results presented here, the corresponding integral representations are
derived for familiar simpler classes of hypergeometric polynomials such as (for example) the Lagrange polynomials, Shively’s
pseudo-Laguerre polynomials, and generalized Bessel polynomials. Each of the integral representations derived in this paper
may be also viewed as a linearization relationship for the product of two different members of the associated family of hypergeometric
polynomials. 相似文献
116.
117.
An evaluation of the CYP2D6 and CYP3A4 inhibition potential of metoprolol metabolites and their contribution to drug–drug and drug–herb interaction by LC‐ESI/MS/MS
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Roshan M. Borkar Murali Mohan Bhandi Ajay P. Dubey V. Ganga Reddy Prashanth Komirishetty Prajwal P. Nandekar Abhay T. Sangamwar Ahmed Kamal Sanjay K. Banerjee R. Srinivas 《Biomedical chromatography : BMC》2016,30(10):1556-1572
The aim of the present study was to evaluate the contribution of metabolites to drug–drug interaction and drug–herb interaction using the inhibition of CYP2D6 and CYP3A4 by metoprolol (MET) and its metabolites. The peak concentrations of unbound plasma concentration of MET, α‐hydroxy metoprolol (HM), O‐desmethyl metoprolol (ODM) and N‐desisopropyl metoprolol (DIM) were 90.37 ± 2.69, 33.32 ± 1.92, 16.93 ± 1.70 and 7.96 ± 0.94 ng/mL, respectively. The metabolites identified, HM and ODM, had a ratio of metabolic area under the concentration–time curve (AUC) to parent AUC of ≥0.25 when either total or unbound concentration of metabolite was considered. In vitro CYP2D6 and CYP3A4 inhibition by MET, HM and ODM study revealed that MET, HM and ODM were not inhibitors of CYP3A4‐catalyzed midazolam metabolism and CYP2D6‐catalyzed dextromethorphan metabolism. However, DIM only met the criteria of >10% of the total drug related material and <25% of the parent using unbound concentrations. If CYP inhibition testing is solely based on metabolite exposure, DIM metabolite would probably not be considered. However, the present study has demonstrated that DIM contributes significantly to in vitro drug–drug interaction. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
118.
Ambrish Kumar Srivastava 《Molecular physics》2018,116(12):1642-1649
Benzene (C6H6) and polycyclic hydrocarbons such as naphthalene (C10H8), anthracene (C14H10) and coronene (C24H12) are well known aromatic organic compounds. We study the substitution of Li replacing all H-atoms in these hydrocarbons using density functional method. The vertical ionisation energy of such lithiated species, i.e. C6Li6, C10Li8, C14Li10 and C24Li12 ranges 4.24–4.50 eV, which is lower than the ionisation energy (IE) of Li atom. Thus, these species may behave as superalkalis due to their lower IE than alkali metal. However, these lithiated species possess planar and closed-shell structure, unlike typical superalkalis. Furthermore, all Li-substituted species are aromatic although their degree of aromaticity is reduced as compared to corresponding hydrocarbon analogues. We have further explored the structure of C6Li6 as star-like, unlike its inorganic analogue B3N3Li6, which appears as fan-like structure. We have also demonstrated that the interaction of C6Li6 with a superhalogen (such as BF4) is similar to that of a typical superalkali (such as OLi3). This may further suggest that the proposed lithiated species may form a new class of closed-shell organic superalkalis with aromaticity. 相似文献
119.
Shashank Shukla Joseph Favata Vikas Srivastava Sina Shahbazmohamadi Anubhav Tripathi Anita Shukla 《Journal of polymer science. Part A, Polymer chemistry》2020,58(10):1365-1379
Developing optimized hydrogel products requires an in-depth understanding of the mechanisms that drive hydrogel tunability. Here, we performed a full 4 × 4 factorial design study investigating the impact of gellan, a naturally derived polysaccharide (1%, 2%, 3%, or 4% w/v) and CaCl2 concentration (1, 3, 7, or 10 mM) on the viscoelastic, swelling, and drug release behavior of gellan hydrogels containing a model drug, vancomycin. These concentrations were chosen to specifically provide insight into gellan hydrogel behavior for formulations utilizing polymer and salt concentrations expanding beyond those commonly reported by previous studies exploring gellan. With increasing gellan and CaCl2 concentration, the hydrogel storage moduli (0.1–100 kPa) followed a power-law relationship and on average these hydrogels had higher liquid absorption capability and greater total drug release over 6 days. We suggest that the effects of gellan and CaCl2 concentration and their interactions on hydrogel properties can be explained by various phenomena that lead to increased swelling and increased resistance to network expansion. 相似文献
120.
For the first time, intensification of monooleoyl glycerol (MOG) synthesis has been investigated in an ultrasonic-infrared-wave (USIRW) promoted batch reactor. Esterification of octadecanoic acid (ODA) with glycerol (Gl) has been conducted [using Amberlyst 36 wet catalyst] in three different reactors, namely traditional batch reactor (TBR), infrared wave promoted batch reactor (IRWPBR), and USIRW-promoted batch reactor (USIRWPBR) to assess the relative efficacy. The energy-efficient USIRWPBR remarkably intensifies the ODA-Gl esterification as manifested through superior ODA conversion (92.5 ± 1.25%) compared to that achieved in IRWPBR (79.8 ± 1.2%) and TBR (36.39 ± 1.25%). The most favorable reaction condition for optimum ODA conversion and maximum MOG yield was identified through statistical optimization over a selected parametric range, namely 3-5 Gl/ODA mole ratio, 0.004-0.006 g/mL Amberlyst 36 catalyst concentration, 300-700 rpm impeller speed, and 333-353 K reaction temperature. The present study also reports the formulation and validation of an innovative reaction kinetics, that is, concurrent noncatalytic and heterogeneously catalyzed (CNCHC) reaction mechanism in addition to the conventional heterogeneous kinetic models (LH and Eley-Rideal mechanisms). Under combined USIRW, the CNCHC esterification mechanism could best describe ODA-Gl esterification (R2 = 0.98) compared to LH (R2 = 0.97) and Eley-Rideal (R2 = 0.88) mechanisms. The optimal product (MOG) was characterized by differential scanning calorimetry and thermogravimetric analysis to assess its crystallization property and thermal stability for possible application as plasticizer/fuel additives. 相似文献