全文获取类型
收费全文 | 33276篇 |
免费 | 256篇 |
国内免费 | 303篇 |
专业分类
化学 | 13579篇 |
晶体学 | 306篇 |
力学 | 1453篇 |
综合类 | 12篇 |
数学 | 9568篇 |
物理学 | 8917篇 |
出版年
2022年 | 104篇 |
2021年 | 139篇 |
2020年 | 129篇 |
2019年 | 120篇 |
2018年 | 1291篇 |
2017年 | 1508篇 |
2016年 | 868篇 |
2015年 | 673篇 |
2014年 | 619篇 |
2013年 | 890篇 |
2012年 | 3402篇 |
2011年 | 2669篇 |
2010年 | 1975篇 |
2009年 | 1695篇 |
2008年 | 820篇 |
2007年 | 851篇 |
2006年 | 842篇 |
2005年 | 4632篇 |
2004年 | 4069篇 |
2003年 | 2437篇 |
2002年 | 607篇 |
2001年 | 336篇 |
2000年 | 158篇 |
1999年 | 214篇 |
1998年 | 138篇 |
1997年 | 112篇 |
1996年 | 110篇 |
1995年 | 94篇 |
1994年 | 71篇 |
1993年 | 59篇 |
1992年 | 207篇 |
1991年 | 189篇 |
1990年 | 159篇 |
1989年 | 127篇 |
1988年 | 125篇 |
1987年 | 78篇 |
1986年 | 62篇 |
1985年 | 69篇 |
1984年 | 55篇 |
1983年 | 48篇 |
1982年 | 56篇 |
1981年 | 51篇 |
1979年 | 53篇 |
1978年 | 51篇 |
1976年 | 99篇 |
1975年 | 55篇 |
1974年 | 55篇 |
1973年 | 66篇 |
1972年 | 46篇 |
1966年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Yongya Li Hayam Mansour Colton J. F. Watson Yanan Tang Adam J. MacNeil Feng Li 《Chemical science》2021,12(6):2133
Herein, we describe an isothermal proximity CRISPR Cas12a assay that harnesses the target-induced indiscrimitive single-stranded DNase activity of Cas12a for the quantitative profiling of gene expression at the mRNA level and detection of proteins with high sensitivity and specificity. The target recognition is achieved through proximity binding rather than recognition by CRISPR RNA (crRNA), which allows for flexible assay design. A binding-induced primer extension reaction is used to generate a predesigned CRISPR-targetable sequence as a barcode for further signal amplification. Through this dual amplification protocol, we were able to detect as low as 1 fM target nucleic acid and 100 fM target protein isothermally. The practical applicability of this assay was successfully demonstrated for the temporal profiling of interleukin-6 gene expression during allergen-mediated mast cell activation.Herein, we develop an isothermal proximity CRISPR Cas12a assay that harnesses the target-induced collateral cleavage activity of Cas12a for the quantitative profiling of gene expression and detection of proteins with high sensitivity and specificity. 相似文献
982.
Castellano PM Vignaduzzo SE Maggio RM Kaufman TS 《Analytical and bioanalytical chemistry》2005,382(7):1711-1714
A new, repeatable, and rapid method has been developed for resolution of binary mixtures of acetaminophen and diclofenac with minimum sample pretreatment and without separation of the analytes. The method, based on the PLS1 processing of absorbance data in the UV region, was successfully used for quantification of the drug content of three tablet preparations. The results obtained were in good agreement with HPLC recovery data. The method also enabled determination of drug-dissolution profiles of these commercial tablets, by simultaneous determination of both analytes during the dissolution test. 相似文献
983.
Zoya?Orekhova Yonit?SambiraEmail author Emanuel?Manzurola Alexander?Apelblat 《Journal of solution chemistry》2005,34(7):853-867
Conductivity measurements of DL-pyroglutamic acid and sodium pyroglutamate in dilute aqueous solutions were performed in the 288.15–323.15 K temperature range. The limiting molar conductances of pyroglutamate anion, λo(pGlu−, T) and the dissociation constants of pyroglutamic acid, K(T) were derived from the Onsager, and the Quint and Viallard conductivity equations. Densities of aqueous solutions with molalities lower than 0.5 mol-kg−1 were determined at 5 K intervals from T = 288.15 K to 333.15 K. Densities served to evaluate the apparent molar volumes, V2,φ(m, T), the cubic expansion coefficients, α (m,T) and the changes of the isobaric heat capacities with respect to pressure, (∂ CP/∂ P)T,m. They were correlated qualitatively with the changes in the structure of water when pyroglumatic acid is dissolved in it. 相似文献
984.
Xia Y Wu J McLuckey SA Londry FA Hager JW 《Journal of the American Society for Mass Spectrometry》2005,16(1):71-81
Ion/ion proton transfer reactions involving mutual storage of both ion polarities in a linear ion trap (LIT) that comprises part of a hybrid triple quadrupole/linear ion trap mass spectrometer have been effected. Mutual ion storage in the x- and y-dimensions arises from the normal operation of the oscillating quadrupole field of the quadrupole array, while storage in the z-dimension is enabled by applying unbalanced radio-frequency amplitudes to opposing sets of rods of the array. Efficient trapping (>90%) is achieved for thermalized ions over periods of several seconds. Reactions were demonstrated for multiply charged protein/peptide cations formed by electrospray with anions derived from glow discharge ionization of perfluoro(methyldecalin) (PMD) introduced from the side of the LIT rod array. Doubly and singly charged protein ions are readily formed via ion/ion reactions. The parameters that affect ion/ion reactions are discussed, including the degree of RF unbalance on the LIT rods, vacuum pressure, nature of the buffer gas, reaction time, anion abundance, and the low mass cutoff for ion/ion reaction. The present system has a demonstrated upper mass-to-charge ratio limit of at least 33,000. The system also has high flexibility with respect to defining MS(n) experiments involving both collision-induced dissociation (CID) and ion/ion reactions. Experiments are demonstrated involving beam-type CID in the pressurized collision quadrupole (Q2) followed by ion/ion reactions involving the product ions in the LIT. Ion parking experiments are also demonstrated using the mutual storage ion/ion reaction mode in the LIT, with a parking efficiency over 60%. 相似文献
985.
Many aspects of the behavior of surfactants have not been well understood due to the coupling of many different mechanisms.
Computer simulation is, therefore, attractive in the sense that it can explore the effect of different mechanisms separately.
In this paper, the shapes, structures and sizes of sodium dodecylbenzenesulfonate (SDBS) micelles under different concentrations
in an oil/water mixture were studied via molecular dynamics (MD) simulations using a simplified atomistic model which basically
maintains the hydrophile and lipophile properties of the surfactant molecules. Above the critical micellar concentration (cmc),
surfactant molecules aggregate spontaneously to form a wide variety of assemblies, from spherical to rodlike, wormlike and
bilayer micelles. Changes in their ratios of the principle moments of inertia (g1/g3, g2/g3) indicated the transition of micelle shapes at different concentrations. The aggregation number of micelle is found to have
a power-law dependence on surfactant concentration. 相似文献
986.
Zinc(II) and mercury(II) complexes were prepared by reacting isatin-3-thiosemicarbazone (ISTSCH) with zinc(II) acetate or mercury(II) bromide. The complexes were characterized by IR, Raman, diffuse reflectance, 1H and 13C NMR spectra and elemental analysis. Tetrahedral structures for Zn(ISTSC)2 and Hg(ISTSCH)Br2 are suggested. 相似文献
987.
Wojakowska A. Krzyżak E. Wojakowski A. 《Journal of Thermal Analysis and Calorimetry》2001,65(2):491-495
The phase diagram for the RbBr–CuBr system has been determined. In the system two intermediate compounds are formed: RbCu2Br3, melting congruently at 537 K and Rb3CuBr4, melting incongruently at 544 K. The coordinates of the two eutectic points are: 501 K, 54 mole% CuBr and 522 K, 74 mole%
CuBr.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
988.
Rakesh?Kumar?MahajanEmail author Jyoti?Chawla Mandeep?Singh?BakshiEmail author 《Colloid and polymer science》2004,282(10):1165-1168
Cloud point (CP) measurements of Tween 20 and Tween 80 were carried out in the presence of various glycol oligomers and triblock polymers (TBP). The cloud points of both Tween 20 and 80 decrease in the presence of both types of additives. Among the glycol oligomeric additives, ethylene glycol monobutyl ether was found to reduce the CP maximum. An increase in the repeating units of polymeric glycol additives leads to a decrease in CP. Reduction in the CP in the presence of TBP depends upon the increase in hydrophobic/hydrophilic ratio among the polypropylene to polyethylene units. 相似文献
989.
Paints and coatings are frequently encountered as types of materials that are submitted to forensic science laboratories as a result of trace evidence transfers. The aim of this study was to develop a method to complement the commonly used techniques in a forensic laboratory in order to better characterize these samples for forensic purposes. A laser ablation method has been used to simultaneously sample several layers directly prior to introduction into an inductively coupled plasma-mass spectrometer for the detection and quantification of the trace metals present in the layer(s). Time-resolved analysis plots displaying the elemental response and quantification of selected metals are compared to associate/discriminate paint samples. Matrix-matched standards were successfully incorporated into the analysis scheme for quantification of lead in the solid paint samples. Preparation of new matrix-matched standards for quantification of additional elements developed for this study are also presented. A sample set of eighteen (18) survey automotive paint samples have been analyzed with the developed method in order to determine the utility of LA-ICP-MS for trace element analysis of paints. 相似文献
990.
Barrett B Borek-Dohalský V Fejt P Vaingátová S Huclová J Nemec B Jelínek I 《Analytical and bioanalytical chemistry》2005,383(2):210-217
A validated, highly sensitive, and selective HPLC method with MS–MS detection has been developed for quantitative determination
of azithromycin (AZI) in human Na2EDTA plasma. Roxithromycin (ROX) was used as internal standard. Human plasma containing AZI and internal standard was ultrafiltered
through Centrifree Micropartition devices and the concentration of AZI was determined by isocratic HPLC–MS–MS. Multiple reaction
monitoring mode (MRM) was used for MS–MS detection. The calibration plot was linear in the concentration range 2.55–551.43 ng mL−1. Inter-day and Intra-day precision and accuracy of the proposed method were characterized by R.S.D and percentage deviation,
respectively; both were less than 8%. Limit of quantification was 2.55 ng mL−1. The proposed method was used to determine the pharmacokinetic profile of AZI (250-mg tablets). 相似文献