全文获取类型
收费全文 | 1723篇 |
免费 | 46篇 |
国内免费 | 5篇 |
专业分类
化学 | 1066篇 |
晶体学 | 10篇 |
力学 | 24篇 |
数学 | 233篇 |
物理学 | 441篇 |
出版年
2022年 | 13篇 |
2021年 | 16篇 |
2020年 | 21篇 |
2019年 | 21篇 |
2016年 | 25篇 |
2015年 | 27篇 |
2014年 | 27篇 |
2013年 | 76篇 |
2012年 | 79篇 |
2011年 | 91篇 |
2010年 | 61篇 |
2009年 | 36篇 |
2008年 | 73篇 |
2007年 | 84篇 |
2006年 | 78篇 |
2005年 | 68篇 |
2004年 | 95篇 |
2003年 | 55篇 |
2002年 | 55篇 |
2001年 | 48篇 |
2000年 | 51篇 |
1999年 | 26篇 |
1998年 | 28篇 |
1997年 | 18篇 |
1996年 | 21篇 |
1995年 | 23篇 |
1994年 | 29篇 |
1993年 | 45篇 |
1992年 | 35篇 |
1991年 | 27篇 |
1990年 | 18篇 |
1989年 | 26篇 |
1988年 | 23篇 |
1987年 | 9篇 |
1986年 | 18篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 18篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 17篇 |
1978年 | 21篇 |
1977年 | 14篇 |
1976年 | 25篇 |
1975年 | 16篇 |
1974年 | 10篇 |
1973年 | 11篇 |
1972年 | 10篇 |
1971年 | 10篇 |
排序方式: 共有1774条查询结果,搜索用时 15 毫秒
91.
There is an ongoing debate regarding the mechanism of Pt electrochemical dissolution. However, only off-line methods have so far been used, where separation of Pt species is performed separately from their detection. In this study, ion exchange chromatography coupled to inductively coupled plasma mass spectrometry was used for the first time to separate and detect Pt species generated by the electro-dissolution of a Pt electrode in 0.5 M aqueous H2SO4 solution. Because these species are either neutral or cationic, they were converted to chloro-complexes using 0.1 M KCl to enable their separation by anion exchange chromatography. Chloro-aqua complexes were observed in addition to the two predominant species, namely PtCl42− and PtCl62−. A good linear relationship was observed between the sum of peak areas for all complexes of a given Pt oxidation state and the Pt concentration, with a detection limit of 0.1 μg L−1 being reached for Pt(II) and Pt(IV). Application of this speciation analysis method to real samples generated by potential cycling using cyclic voltammetry (CV) revealed that, in general, at least 80% of Pt was present as Pt(II), irrespectively of the cyclic potential range or of temperature (up to 60 °C). Still, quantitative spike recovery was achieved after adding known amounts of Pt(II) or Pt(IV) to a sample prepared by CV, which demonstrated that no significant species inter-conversion took place. 相似文献
92.
A method for the synthesis of sultam thioureas via a different 1,4,2-dithiazolidine 1,1-dioxide ring-forming reaction is presented here. The syntheses of nine sultam thioureas were achieved in 53–81% yield by reacting N-substituted chloromethanesulfonamides with thiocarbamoyl isothiocyanates, which were formed in situ from the reaction of 5-(disubstituted amino)-3H-1,2,4-dithiazole-3-thiones with triphenylphosphine. Importantly, this method successfully allowed the substituent of the ring nitrogen atom to be varied. Additionally, the structures of four sultam thioureas were confirmed by x-ray diffraction. 相似文献
93.
The chemical versatility of 2,4(3H,5H)-furandione (β-tetronic acid, 1) and its synthetic applicability are of considerable current interest1b,2a-k. The multifunctional character of this small molecule confers an intriguing synthetic potential which has prompted us to develop synthetic schemes utilizing it as a synthon for certain heterocyclic systems. 相似文献
94.
A convenient synthesis and resolution of (-)-trans-4aR,8aR-1-propyl-6-oxo-decahydroquinoline (4) is described. This compound is then converted into the D-2 selective dopamine agonist, (-)-quinpirole hydrochloride (3). 相似文献
95.
Ryan M. Tipker Jake A. Muldoon Daniel H. Pham Balazs R. Varga Russell P. Hughes David S. Glueck Gary J. Balaich Arnold L. Rheingold 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2022,134(1):e202110753
Tetrahedral main-group compounds are normally configurationally stable, but P-epimerization of the chiral phosphiranium cations syn- or anti-[Mes*P(Me)CH2CHPh][OTf] (Mes*=2,4,6-(t-Bu)3C6H2) occurred under mild conditions at 60 °C in CD2Cl2, resulting in isomerization to give a syn-enriched equilibrium mixture. Ion exchange with excess [NBu4][Δ-TRISPHAT] (Δ-TRISPHAT=Δ-P(o-C6Cl4O2)3) followed by chromatography on silica removed [NBu4][OTf] and gave mixtures of syn- and anti-[Mes*P(Me)CH2CHPh][Δ-TRISPHAT]?x[NBu4][Δ-TRISPHAT]. NMR spectroscopy showed that isomerization proceeded with epimerization at P and retention at C. DFT calculations are consistent with a mechanism involving P-C cleavage to yield a hyperconjugation-stabilized carbocation, pyramidal inversion promoted by σ-interaction of the P lone pair with the neighboring β-carbocation, and ring closure with inversion of configuration at P. 相似文献
96.
Dr. Andrea Hornemann Dr. Diane M. Eichert Arne Hoehl Dr. Brigitte Tiersch Prof. Gerhard Ulm Prof. Maxim G. Ryadnov Dr. Burkhard Beckhoff 《Chemphyschem》2022,23(4):e202100815
Synchrotron radiation-based Fourier transform infrared spectroscopy enables access to vibrational information from mid over far infrared to even terahertz domains. This information may prove critical for the elucidation of fundamental bio-molecular phenomena including folding-mediated innate host defence mechanisms. Antimicrobial peptides (AMPs) represent one of such phenomena. These are major effector molecules of the innate immune system, which favour attack on microbial membranes. AMPs recognise and bind to the membranes whereupon they assemble into pores or channels destabilising the membranes leading to cell death. However, specific molecular interactions responsible for antimicrobial activities have yet to be fully understood. Herein we probe such interactions by assessing molecular specific variations in the near-THz 400–40 cm−1 range for defined helical AMP templates in reconstituted phospholipid membranes. In particular, we show that a temperature-dependent spectroscopic analysis, supported by 2D correlative tools, provides direct evidence for the membrane-induced and folding-mediated activity of AMPs. The far-FTIR study offers a direct and information-rich probe of membrane-related antimicrobial interactions. 相似文献
97.
Ricardo G. Alvim Petrina Georgala Lucas Nogueira Alexander J. Somma Karan Nagar Jasmine Thomas Laura Alvim Amelia Riegel Christopher Hughes Jie Chen Augusto B. Reis Souhil Lebdai Avigdor Scherz Steven Zanganeh Rui Gardner Kwanghee Kim Jonathan A. Coleman 《Molecules (Basel, Switzerland)》2021,26(12)
Purpose: Vascular targeted photodynamic therapy (VTP) is a nonsurgical tumor ablation approach used to treat early-stage prostate cancer and may also be effective for upper tract urothelial cancer (UTUC) based on preclinical data. Toward increasing response rates to VTP, we evaluated its efficacy in combination with concurrent PD-1 inhibitor/OX40 agonist immunotherapy in a urothelial tumor-bearing model. Experimental design: In mice allografted with MB-49 UTUC cells, we compared the effects of combined VTP with PD-1 inhibitor/OX40 agonist with those of the component treatments on tumor growth, survival, lung metastasis, and antitumor immune responses. Results: The combination of VTP with both PD-1 inhibitor and OX40 agonist inhibited tumor growth and prolonged survival to a greater degree than VTP with either immunotherapeutic individually. These effects result from increased tumor infiltration and intratumoral proliferation of cytotoxic and helper T cells, depletion of Treg cells, and suppression of myeloid-derived suppressor cells. Conclusions: Our findings suggest that VTP synergizes with PD-1 blockade and OX40 agonist to promote strong antitumor immune responses, yielding therapeutic efficacy in an animal model of urothelial cancer. 相似文献
98.
Chen X Zhang L Zhou K Davies E Sugden K Bennion I Hughes M Hine A 《Optics letters》2007,32(17):2541-2543
Using an optical biosensor based on a dual-peak long-period fiber grating, we have demonstrated the detection of interactions between biomolecules in real time. Silanization of the grating surface was successfully realized for the covalent immobilization of probe DNA, which was subsequently hybridized with the complementary target DNA sequence. It is interesting to note that the DNA biosensor was reusable after being stripped off the hybridized target DNA from the grating surface, demonstrating a function of multiple usability. 相似文献
99.
We apply random matrix theory to compare correlation matrix estimators C obtained from emerging market data. The correlation matrices are constructed from 10 years of daily data for stocks listed on the Johannesburg stock exchange (JSE) from January 1993 to December 2002. We test the spectral properties of C against random matrix predictions and find some agreement between the distributions of eigenvalues, nearest neighbour spacings, distributions of eigenvector components and the inverse participation ratios for eigenvectors. We show that interpolating both missing data and illiquid trading days with a zero-order hold increases agreement with RMT predictions. For the more realistic estimation of correlations in an emerging market, we suggest a pairwise measured-data correlation matrix. For the data set used, this approach suggests greater temporal stability for the leading eigenvectors. An interpretation of eigenvectors in terms of trading strategies is given, as opposed to classification by economic sectors. 相似文献
100.
“CLASSIC NMR”: An In‐Situ NMR Strategy for Mapping the Time‐Evolution of Crystallization Processes by Combined Liquid‐State and Solid‐State Measurements
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Colan E. Hughes P. Andrew Williams Prof. Kenneth D. M. Harris 《Angewandte Chemie (International ed. in English)》2014,53(34):8939-8943
A new in‐situ NMR strategy (termed CLASSIC NMR) for mapping the evolution of crystallization processes is reported, involving simultaneous measurement of both liquid‐state and solid‐state NMR spectra as a function of time. This combined strategy allows complementary information to be obtained on the evolution of both the solid and liquid phases during the crystallization process. In particular, as crystallization proceeds (monitored by solid‐state NMR), the solution state becomes more dilute, leading to changes in solution‐state speciation and the modes of molecular aggregation in solution, which are monitored by liquid‐state NMR. The CLASSIC NMR experiment is applied here to yield new insights into the crystallization of m‐aminobenzoic acid. 相似文献