全文获取类型
收费全文 | 5056篇 |
免费 | 790篇 |
国内免费 | 1080篇 |
专业分类
化学 | 5132篇 |
晶体学 | 65篇 |
力学 | 152篇 |
综合类 | 37篇 |
数学 | 25篇 |
物理学 | 1515篇 |
出版年
2024年 | 14篇 |
2023年 | 98篇 |
2022年 | 123篇 |
2021年 | 165篇 |
2020年 | 249篇 |
2019年 | 195篇 |
2018年 | 154篇 |
2017年 | 187篇 |
2016年 | 284篇 |
2015年 | 245篇 |
2014年 | 309篇 |
2013年 | 597篇 |
2012年 | 414篇 |
2011年 | 428篇 |
2010年 | 347篇 |
2009年 | 387篇 |
2008年 | 346篇 |
2007年 | 377篇 |
2006年 | 324篇 |
2005年 | 312篇 |
2004年 | 263篇 |
2003年 | 205篇 |
2002年 | 184篇 |
2001年 | 113篇 |
2000年 | 78篇 |
1999年 | 58篇 |
1998年 | 76篇 |
1997年 | 55篇 |
1996年 | 68篇 |
1995年 | 61篇 |
1994年 | 27篇 |
1993年 | 20篇 |
1992年 | 23篇 |
1991年 | 22篇 |
1990年 | 17篇 |
1989年 | 19篇 |
1988年 | 10篇 |
1987年 | 5篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1972年 | 2篇 |
1970年 | 2篇 |
排序方式: 共有6926条查询结果,搜索用时 31 毫秒
51.
Navjeet Kaur Yamini Verma Pooja Grewal Neha Ahlawat Pranshu Bhardwaj Nirmala Kumari Jangid 《合成通讯》2020,50(9):1286-1334
AbstractFew conversions cannot take place with ground-state reactions even with the help of a catalyst, therefore they are made to occur under photochemical conditions. The transfer of electrons took place even with the photochemical excitement of one molecule where redox reaction cannot occur at the ground state. The ground-state reactions resulted in the formation of side products. The substrates did not require any sort of chemical activation for C–N bond construction in the course of photochemical reactions. The source of energy; light has always been the interest of researchers in order to induce chemical reactions ever since the starting of scientific chemistry. The present review encloses the chemistry of photochemical transformations with a focus on their synthetic uses. The organic photochemical reactions prevent the polluting or harmful reagents thus, provides a possibility for sustainable procedures as well as green chemistry. This review article displays the formation of numerous of five-membered fused nitrogen-heterocyclic compounds. 相似文献
52.
M. Frederick Hawthorne 《Angewandte Chemie (International ed. in English)》1993,32(7):950-984
A therapeutic method that selectively destroys malignant cells in the presence of normal cells is a highly valued goal of oncologists and the possible salvation of cancer patients afflicted with some incurable forms of the disease. Selective cell destruction is, in principle, possible with a binary therapeutic strategy based upon the neutron capture reaction observed with the 10B nucleus and a neutron of low kinetic energy (thermal neutron). This nuclear fission reaction produces both 4He and 7Li+ nuclei along with about 2.4 MeV of kinetic energy and weak γ-radiation. Since the energetic and cytotoxic product ions travel only about one cell diameter in tissue one may specify the cell type to be destroyed by placing innocent 10B nuclei on or within only the doomed cells. This article describes the current status of chemical research aimed at the eventual adoption of this therapeutic method (boron neutron capture therapy or BNCT). The multidisciplinary nature of this research effort involves chemistry, biology, nuclear physics, medicine, and related specialties. Methods devised for bringing 10B nuclei to tumor cells in therapeutic amounts are correlated with the structure of a generalized cell and the various cellular compartments available for boron localization. The synthesis methods employed for the creation of boron-containing biomolecules and drugs are presented along with representative data concerning their efficacy in tumor localization. The outlook for BNCT is especially bright at this time because of rapid developments in the fields of bioorganometallic chemistry, microbiology, immunology, and nuclear science, to name but a few. Very effective boron delivery vehicles have been demonstrated, and through the interaction of chemistry and biology these species are undergoing further improvement and evaluation of their suitability for BNCT. 相似文献
53.
54.
Y. Shacham-Diamand Y. Sverdlov V. Bogush R. Ofek-Almog 《Journal of Solid State Electrochemistry》2007,11(7):929-938
Thin cobalt alloy films have been obtained using electroless deposition solution with two reducing agents: dimethylamine borane
(DMAB) and sodium hypophosphite. This system allows spontaneous and self-activated deposition of barrier layers on Cu lines
and via contacts for ultra large scale integration (ULSI) interconnects applications. This work presents a study of the solution
composition effects on the material properties and composition of the films. First, we present the deposition rates, the electrical
resistance, the various element profiles in the thin film, and the thin film roughness. Next, we discuss the film’s composition
and its dependence on the ratio between the reducing agents composition in the solution. The experimental results suggest
that the film phosphorous and boron composition is determined by the surface adsorption rates of the reducing agents. Therefore,
a surface co-adsorption model of the two reducing agents is proposed, formulated, analyzed, and compared to the experimental
results. Finally, we discuss the model and its significance to the formation of high-quality ultra-thin barrier layers.
Dedicated to Professor Dr. Algirdas Vaskelis on the occasion of his 70th birthday. 相似文献
55.
It is the first time that boron is determined in the presence of a little methanol by discoloring spectrophotometry in this paper. A russety product can be formed by the reaction between glycine (Gly) and sodium 1,2-naphthoquinone-4-sulfonate (NQS) in alkaline solution. When boron is added to the solution, the system will be discolored, and the addition of a little methanol will improve the discoloration. Beer's law is obeyed in the range of boron concentrations of 0.86-43.24 μg ml−1 at the maximal discoloring wavelength of 382 nm. The equation of linear regression is A = −0.07581-86.79186C (mol l−1), with a linearly correlation coefficient of 0.9979. The detection limit is 0.80 μg ml−1 and R.S.D. is 4.2%. The method is successfully applied to the determination of boron in pharmaceutical and biological samples. The average recoveries are in the range of 98.2-104.1%. Analytical results obtained with this novel method are satisfactory. 相似文献
56.
《Electroanalysis》2004,16(16):1285-1291
The electrochemical oxidation of the cysteine‐quinone adduct has been examined as a means of providing an electroanalytical cysteine specific detection protocol. The appliance of square‐wave voltammetry allowed 0.5 μM as a limit of detection. The effects of various biologically relevant interferences including other thiols were studied and found to present no change in the voltammetric profile. The practical applicability and efficiency of the methodology was probed through the determination of cysteine concentration in growth tissue medium. 相似文献
57.
Classifying wine according to geographical origin via quadrupole-based ICP–mass spectrometry measurements of boron isotope ratios 总被引:1,自引:0,他引:1
The potential of quadrupole-based ICP–MS as a tool for B-isotopic analysis of wines and its usefulness in provenance determinations
were assessed. A precision of 0.1–0.25% RSD (corresponding to a relative standard deviation of the mean of three replicate
measurements of 0.06–0.12%) was sufficient to establish small differences in the B isotope ratios in wines from different
geographical origins. Each sample measurement was bracketed by measurements of a standard and mass bias drift correction made
by interpolation. Sample preparation was kept to a minimum to avoid possible fractionation. Dilution of the wine samples by
a factor of 100 with 0.65% HNO3 was found to reduce matrix-induced mass discrimination substantially. Wines from three wine-producing regions, Stellenbosch,
Robertson, and Swartland, in the Western Cape Province of South Africa, and wines from specific regions in France (Bergerac)
and Italy (Valpolicella) were analyzed by ICP–QMS for their B-isotopic compositions. It was concluded that the 11B/10B ratios can be used to characterize wines from different geographical origins. Average 11B/10B ratios in red wines from South Africa (Stellenbosch), France (Bergerac), and Italy (Valpolicella) were found to differ by
between 0.5 and 1.5%. 相似文献
58.
Kang Y Zyryanov GV Rudkevich DM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(6):1924-1932
The use of simple calix[4]arenes for chemical conversion of NO2/N2O4 gases is demonstrated in solution and in the solid state. Upon reacting with these gases, calixarenes 1 encapsulate nitrosonium (NO+) cations within their cavities with the formation of stable calixarene-NO+ complexes 2. These complexes act as encapsulated nitrosating reagents; cavity effects control their reactivity and selectivity. Complexes 2 were effectively used for nitrosation of secondary amides 5, including chiral derivatives. Unique size-shape selectivity was observed, allowing for exclusive nitrosation of less crowded N-Me amides 5 a-e (up to 95 % yields). Bulkier N-Alk (Alk>Me) substrates 5 did not react due to the hindered approach to the encapsulated NO+ reagents. Robust, silica gel based calixarene material 3 was prepared, which reversibly traps NO2/N2O4 with the formation of NO+-storing silica gel 4. With material 4, similar size-shape selectivity was observed for nitrosation. The N-Me-N-nitroso derivatives 6 d,e were obtained with approximately 30 % yields, while bulkier amides were nitrosated with much lower yields (<8 %). Enantiomerically pure encapsulating reagent 2 d was tested for nitrosation of racemic amide 5 t, showing modest but reproducible stereoselectivity and approximately 15 % ee. Given high affinity to NO+ species, which can be generated by a number of NOX gases, these supramolecular reagents and materials may be useful for NOX entrapment and separation in the environment and biomedical areas. 相似文献
59.
For a connected graph G we denote by d(G,k) the number of vertex pairs at distance k. The Hosoya polynomial of G is H(G,x) = ∑k≥0 d(G,k)xk. In this paper, analytical formulae for calculating the polynomials of armchair open‐ended nanotubes are given. Furthermore, the Wiener index, derived from the first derivative of the Hosoya polynomial in x = 1, and the hyper‐Wiener index, from one‐half of the second derivative of the Hosoya polynomial multiplied by x in x = 1, can be calculated. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
60.
构造了氮-镍相互作用的5-参数Morse势,研究了氮原子在Ni(\r\n100),Ni(110)和Ni(111)平坦表面的吸附和振动,获得了氮原子\r\n在三个低指数表面的吸附位、吸附构型、结合能和本征振动等数据,计\r\n算结果与实验结果非常吻合.同时,与Ni(100)表面对比,系统研究\r\n了氮原子在Ni(510)台阶面的吸附和扩散.计算结果表明,氮原子在\r\n台阶下部形成最稳定的吸附态,台阶对下台面上扩散的氮原子形成捕获\r\n势,对上台面上扩散的氮原子形成反射势. 相似文献