全文获取类型
收费全文 | 1810篇 |
免费 | 82篇 |
国内免费 | 15篇 |
专业分类
化学 | 1205篇 |
晶体学 | 13篇 |
力学 | 85篇 |
综合类 | 4篇 |
数学 | 270篇 |
物理学 | 330篇 |
出版年
2023年 | 13篇 |
2022年 | 63篇 |
2021年 | 72篇 |
2020年 | 43篇 |
2019年 | 55篇 |
2018年 | 70篇 |
2017年 | 46篇 |
2016年 | 94篇 |
2015年 | 80篇 |
2014年 | 80篇 |
2013年 | 184篇 |
2012年 | 118篇 |
2011年 | 132篇 |
2010年 | 105篇 |
2009年 | 91篇 |
2008年 | 97篇 |
2007年 | 84篇 |
2006年 | 55篇 |
2005年 | 55篇 |
2004年 | 52篇 |
2003年 | 35篇 |
2002年 | 26篇 |
2001年 | 15篇 |
2000年 | 15篇 |
1999年 | 7篇 |
1998年 | 14篇 |
1997年 | 4篇 |
1996年 | 14篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1990年 | 18篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 13篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 6篇 |
排序方式: 共有1907条查询结果,搜索用时 0 毫秒
991.
Ines Ben Hmad Salma Abdeljalil Walid Saibi Bahia Amouri Ali Gargouri 《Applied biochemistry and biotechnology》2014,172(5):2640-2649
The production profile of cellulases of the mutant strain A19 from the filamentous fungus Stachybotrys microspora was studied in the presence of various carbon sources (glucose, lactose, cellulose, carboxymethylcellulose (CMC), and wheat bran) and a range of medium initial pH (5, 7, and 8). Two extracellular cellulases from the Stachybotrys strain (endoglucanases and β-glucosidases) were monitored by enzymatic assay, sodium dodecyl sulfate–polyacrylamide gel electrophoresis, and zymogram analysis. Glucose and lactose repressed CMCase time course production while they permitted a strong β-glucosidase one. On Avicel cellulose, CMC, and wheat bran, both activities were highly produced. Wheat bran (WB) is the best carbon source with an optimum of production at days 5 and 6. The production kinetics of both activities were shown to depend on the medium initial pH, with a preference for neutral or alkaline pH in the majority of conditions. The exception concerned the β-glucosidase which was much more produced at acidic pH, on glucose and cellulose. Most interestingly, a constitutive and conditional expression of an alkaline endoglucanase was revealed on the glucose-based medium at an initial pH of 8 units. The zymogram analysis confirmed such conclusions and highlighted that carbon sources and the pH of the culture medium directed a differential induction of various endoglucanases and β-glucosidases. 相似文献
992.
Mansoureh Tatari Guinyun Kim Haladhara Naik Abbas Hoseini Ranjbar Kwangsoo Kim Sung Chul Yang Muhammad Zaman Muhammad Sahid Sung Gyun Shin Yong Uk Kye Moo-Hyun Cho 《Journal of Radioanalytical and Nuclear Chemistry》2014,300(1):269-275
The isomeric yield ratios for the natAg(γ,xn)104m,g,106m,gAg reactions with the end-point bremsstrahlung energies of 45- and 55-MeV have been determined by the off-line γ-ray spectrometric technique using 100 MeV electron linac at Pohang accelerator laboratory, Korea. The present data were compared with literature data in comparable compound nucleus from the natAg(γ,xn), natPd(p,xn), and 103Rh(α,xn) reactions to examine the effects of an excitation energy and an input angular momentum. It is observed that the isomeric yield ratios of 104,106Ag in natAg(γ,xn), natPd(p,xn) and 103Rh(α,xn) reactions increase with the end-point bremsstrahlung energy, proton and alpha energy, which indicate the role of excitation energy. It is also found that for the similar compound nucleus at same excitation energy, the isomeric yield ratio of 104m,gAg is higher in the natPd(p,xn) and 103Rh(α,xn) reactions than those in natAg(γ,xn) reaction, which indicate the effect of an input angular momentum. 相似文献
993.
Sloane Evariste Mehdi El Sayed Moussa Hok-Lai Wong Guillaume Calvez Vivian Wing-Wah Yam Christophe Lescop 《无机化学与普通化学杂志》2020,646(13):754-760
The tridentate dpmp ligand was reacted with CuI salt and cyano ligand affording selectively and unexpectedly the polymetallic Cu11 complex 2 along one-step reaction. The formation of this derivative 2 can be explained by self-assembling processes controlled by adaptive coordination-driven supramolecular chemistry. The solid-state photophysical behavior of 2 was studied suggesting TADF properties. 相似文献
994.
The Ramanujan Journal - The aim of this paper is twofold. First, it proves the total positivity of the generalized Pascal triangle (classical and q-analogue versions). Second, it studies of the... 相似文献
995.
In this study, poly(P-phenylenediamine/ZnO) (PpPD/ZnO) nanocomposite (NC) under ultrasonic conditions was synthesized and characterized. The presence of zinc oxide nanoparticles changed the morphology of PpPD considerably as confirmed by SEM observations. Hydrazine electrooxidation at novel modified carbon paste electrodes (CPE) with supported NC was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA) techniques. Obtained results showed that the NC increases the surface catalytic activity of CPE toward hydrazine electrooxidation. The electrocatalytic current density increased linearly with hydrazine concentration, and the detection limit and sensitivity are determined to be 24 μM and 0.172 mA cm?2 mM?1, respectively. As revealed by the EIS measurements, the increased conductivity and decreased R ct are owing to the presence of ZnO NPs in the PpPD matrix. The CA results indicated that hydrazine electrooxidation results in higher steady-state current density on CPE/PpDP/ZnO electrode system compared to the CPE/PpDP and CPE electrodes. 相似文献
996.
An isocyanide‐catalyzed reaction between tetracyanoethylene and various activated CH‐acid compounds to afford the corresponding pyran annulated heterocyclic ring systems, in high yield at room temperature within a few minutes, is described. To the best of our knowledge, this is the first example in which isocyanide functions as only a catalyst but not a reagent. 相似文献
997.
A one-pot, three-component, Mannich condensation of electron-rich aromatic compounds such as 5-methyl-2-hydroxyphenyl sulfide, 2-aminopyrimidine, and various aromatic aldehydes were used to prepare a series of new unsymmetrical multidentate aminophenol ligands. These compounds were synthesized in solvent-free conditions as a fast, simple, convenient, and uncatalyzed method. Details of the reaction conditions are discussed. 相似文献
998.
Trisubstituted imidazoles have been synthesized in very short reaction times with excellent yields in the presence of 1,1,3,3‐N,N,N′,N′‐tetramethylguanidinium trifluoroacetate as an ionic liquid at 100°C. The ionic liquid can be recycled for subsequent reactions without any appreciable loss of efficiency. 相似文献
999.
Environmentally friendly three‐component condensation reactions of an activated C‐H acid, an aldehyde, and alkyl nitriles to afford the corresponding pyran annulated heterocyclic systems in water in good yields, avoiding the addition of any catalyst, are reported. 相似文献
1000.
The oxidative cleavage of oximes has been studied under solvent‐free ion exchange resin (IER) catalysis by sodium bromate using ultrasonic irradiation. Both aldoximes and keto‐oximes selectively converted to the corresponding carbonyl compounds in high yields within short times at room temperature. 相似文献