全文获取类型
收费全文 | 3232篇 |
免费 | 115篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 20篇 |
综合类 | 4篇 |
化学工业 | 560篇 |
金属工艺 | 23篇 |
机械仪表 | 27篇 |
建筑科学 | 126篇 |
矿业工程 | 3篇 |
能源动力 | 48篇 |
轻工业 | 363篇 |
水利工程 | 36篇 |
石油天然气 | 1篇 |
无线电 | 118篇 |
一般工业技术 | 405篇 |
冶金工业 | 1321篇 |
原子能技术 | 10篇 |
自动化技术 | 284篇 |
出版年
2023年 | 35篇 |
2022年 | 87篇 |
2021年 | 94篇 |
2020年 | 58篇 |
2019年 | 53篇 |
2018年 | 66篇 |
2017年 | 54篇 |
2016年 | 60篇 |
2015年 | 51篇 |
2014年 | 67篇 |
2013年 | 130篇 |
2012年 | 119篇 |
2011年 | 173篇 |
2010年 | 143篇 |
2009年 | 145篇 |
2008年 | 172篇 |
2007年 | 139篇 |
2006年 | 122篇 |
2005年 | 106篇 |
2004年 | 101篇 |
2003年 | 86篇 |
2002年 | 83篇 |
2001年 | 51篇 |
2000年 | 61篇 |
1999年 | 63篇 |
1998年 | 141篇 |
1997年 | 103篇 |
1996年 | 95篇 |
1995年 | 90篇 |
1994年 | 84篇 |
1993年 | 70篇 |
1992年 | 40篇 |
1991年 | 16篇 |
1990年 | 34篇 |
1989年 | 33篇 |
1988年 | 39篇 |
1987年 | 31篇 |
1986年 | 19篇 |
1985年 | 26篇 |
1984年 | 12篇 |
1983年 | 26篇 |
1982年 | 7篇 |
1981年 | 16篇 |
1980年 | 9篇 |
1979年 | 15篇 |
1977年 | 14篇 |
1976年 | 44篇 |
1973年 | 9篇 |
1970年 | 8篇 |
1969年 | 7篇 |
排序方式: 共有3349条查询结果,搜索用时 46 毫秒
91.
Elisabetta Murru Anna Lisa Muntoni Claudia Manca Sonia Aroni Marco Pistis Sebastiano Banni Gianfranca Carta 《International journal of molecular sciences》2023,24(1)
Fenofibrate (FBR), an oral medication used to treat dyslipidemia, is a ligand of the peroxisome proliferator-activated receptor α (PPARα), a nuclear receptor that regulates the expression of metabolic genes able to control lipid metabolism and food intake. PPARα natural ligands include fatty acids (FA) and FA derivatives such as palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), known to have anti-inflammatory and anorexigenic activities, respectively. We investigated changes in the FA profile and FA derivatives by HPLC and LC-MS in male C57BL/6J mice fed a standard diet with or without 0.2% fenofibrate (0.2% FBR) for 21 days. Induction of PPARα by 0.2% FBR reduced weight gain, food intake, feed efficiency, and liver lipids and induced a profound change in FA metabolism mediated by parallel enhanced mitochondrial and peroxisomal β-oxidation. The former effects led to a steep reduction of essential FA, particularly 18:3n3, with a consequent decrease of the n3-highly unsaturated fatty acids (HUFA) score; the latter effect led to an increase of 16:1n7 and 18:1n9, suggesting enhanced hepatic de novo lipogenesis with increased levels of hepatic PEA and OEA, which may activate a positive feedback and further sustain reductions of body weight, hepatic lipids and feed efficiency. 相似文献
92.
Donatella Restuccia U. Gianfranco Spizzirri Francesco Puoci Maria Lisa Clodoveo Nevio Picci 《Food Analytical Methods》2017,10(3):704-712
In this work, a performing LC method with evaporative light-scattering detector was described for the analysis of tartaric, malic, ascorbic, citric and succinic acids in fruit juices. The method was optimized and validated in comparison with LC-UV, in terms of accuracy, LODs, LOQs and precision. The successive application to ACE, orange, pear, peach, mulberry and apple juices allowed separation and quantitative determination of organic acids in about 20 min just diluting and filtering the sample before LC determination. In the analysed juices, citric, malic and ascorbic acids were always present, and in all the samples, citric acid was the prevailing acid followed by malic acid except for peach and apple juices where an opposite trend was found. Tartaric and succinic acids were detected at lower concentrations and more rarely, except for peach juices, all containing tartaric acid, and ACE and orange juices, all containing succinic acid. 相似文献
93.
The tetracycline (TC) resistance gene tet(M) was monitored in bacteria isolated from Japanese coastal and off-shore marine sediments. The high rate of occurrence of TC resistant (TC(r)) bacteria (120 microg mL(-1) TC) was observed at frequency ranges between 0.0-0.08% in Tokyo Bay, 1.67-1.82% in Sagami Bay and 0.0-4.35% in the open Pacific Ocean. The tet(M) gene was PCR amplified from the TC(r) isolates, showing 127 of 209 isolates (60.8%) as positive. The rate of occurrence of tet(M) was between 32.0-96.0%, 21.1 -28.0% and 0.0-83.3% in the isolates from Tokyo Bay, Sagami Bay and the open Pacific Ocean, respectively. The tet(M) positive isolates belonged to 4 orders of bacteria. Bacillales was the most dominant order (121 strains) among tet(M) possessing bacteria, followed by Actinomycetales (three strains), Flavobacteriales (one strain) and Pseudomonadales (one strain). This indicates that tet(M) is present in various bacterial species and suggests that marine sediments are a natural reservoir of the tet(M) gene. Nucleotide sequence of the tet(M) revealed that two genotypes of tet(M) were found in the bacteria. The two genotypes were placed in genetically distant branches of the phylogenetic tree, suggesting that the two tet(M)s have different origins. 相似文献
94.
Julie K. Furmick Dr. Ichiro Kaneko Angela N. Walsh Joanna Yang Jaskaran S. Bhogal Geoffrey M. Gray Juan C. Baso Drew O. Browder Jessica L. S. Prentice Luis A. Montano Chanh C. Huynh Lisa M. Marcus Dorian G. Tsosie Jungeun S. Kwon Alexis Quezada Nicole M. Reyes Brittney Lemming Puneet Saini Dr. Arjan van der Vaart Dr. Thomas L. Groy Dr. Pamela A. Marshall Dr. Peter W. Jurutka Dr. Carl E. Wagner 《ChemMedChem》2012,7(9):1551-1566
95.
We study finitely generated and finite systems defined by linear partial difference equations with constant coefficients in a Noetherian ring. The two notions coincide for finite rings, and we show that all finite systems exhibit certain periodicity properties. For the particular case of systems over the ring of integers modulo m?>?1, which is important in coding theory, a method is given for determining the number of trajectories, using Gr?bner basis techniques. 相似文献
96.
Fang Liang Jorge Lehr Lisa Danielczak Richard Leask Anne-Marie Kietzig 《International journal of molecular sciences》2014,15(8):13681-13696
Nature shows many examples of surfaces with extraordinary wettability, which can often be associated with particular air-trapping surface patterns. Here, robust non-wetting surfaces have been created by femtosecond laser ablation of polytetrafluoroethylene (PTFE). The laser-created surface structure resembles a forest of entangled fibers, which support structural superhydrophobicity even when the surface chemistry is changed by gold coating. SEM analysis showed that the degree of entanglement of hairs and the depth of the forest pattern correlates positively with accumulated laser fluence and can thus be influenced by altering various laser process parameters. The resulting fibrous surfaces exhibit a tremendous decrease in wettability compared to smooth PTFE surfaces; droplets impacting the virgin or gold coated PTFE forest do not wet the surface but bounce off. Exploratory bioadhesion experiments showed that the surfaces are truly air-trapping and do not support cell adhesion. Therewith, the created surfaces successfully mimic biological surfaces such as insect wings with robust anti-wetting behavior and potential for antiadhesive applications. In addition, the fabrication can be carried out in one process step, and our results clearly show the insensitivity of the resulting non-wetting behavior to variations in the process parameters, both of which make it a strong candidate for industrial applications. 相似文献
97.
Multiple-bonded iron-oxo and -nitrido species have been identified or proposed as key intermediates in a range of important chemical transformations. The reported model complexes feature various coordination geometries and distinct electronic structures, and therefore exhibit diverse reactivity. The present contribution highlights the synergy from both experimental and theoretical standpoints to elucidate their different bonding situations and delineate their common mechanistic features in hydrogen-atom abstraction processes. Our analysis reveals that a radical centered on the abstracting atom E (E=O, N), which is generated via homolysis of covalent Fe−E bonds upon approaching the transition state, is an intrinsic C−H cleaving agent. The iron-oxo species is predicted to be more reactive than its nitride congener, in general, because the O−H bond formed in the H-atom transfer process is often stronger than the corresponding N−H bond. 相似文献
98.
Jennifer Therkorn David Drewry III Thomas Pilholski Kathryn Shaw‐Saliba Gregory Bova Lisa L. Maragakis Brian Garibaldi Lauren Sauer 《Indoor air》2019,29(1):143-155
Biocontainment units (BCUs) are facilities used to care for patients with highly infectious diseases. However, there is limited guidance on BCU protocols and design. This study presents the first investigation of how HVAC (heating, ventilation, air‐conditioning) operating conditions influence the dissemination of fluorescent tracer particles released in a BCU. Test conditions included normal HVAC operation and exhaust failure resulting in loss of negative pressure. A suspension of optical brightener powder and water was nebulized to produce fluorescent particles simulating droplet nuclei (0.5‐5 μm). Airborne particle number concentrations were monitored by Instantaneous Biological Analyzers and Collectors (FLIR Systems). During normal HVAC operation, fluorescent tracer particles were contained in the isolation room (average concentration = 1 × 104 ± 3 × 103/Lair). Under exhaust failure, the automated HVAC system maximizes airflow into areas adjacent to isolation rooms to attempt to maintain negative pressure differential. However, 6% of the fluorescent particles were transported through cracks around doors/door handles out of the isolation room via airflow alone and not by movement of personnel or doors. Overall, this study provides a systematic method for evaluating capabilities to contain aerosolized particles during various HVAC scenarios. Recommendations are provided to improve situation‐specific BCU safety. 相似文献
99.
Dr. Lisa C. Kühnel Dr. Bettina M. Nestl Prof. Dr. Bernhard Hauer 《Chembiochem : a European journal of chemical biology》2017,18(22):2222-2225
Squalene–hopene cyclases (SHCs) catalyze the polycyclization of squalene into a mixture of hopene and hopanol. Recently, amino-acid residues lining the catalytic cavity of the SHC from Alicyclobacillus acidocaldarius were replaced by small and large hydrophobic amino acids. The alteration of leucine 607 to phenylalanine resulted in increased enzymatic activity towards the formation of an intermolecular farnesyl–farnesyl ether product from farnesol. Furthermore, the addition of small-chain alcohols acting as nucleophiles led to the formation of non-natural ether-linked terpenoids and, thus, to significant alteration of the product pattern relative to that obtained with the wild type. It is proposed that the mutation of leucine at position 607 may facilitate premature quenching of the intermediate by small alcohol nucleophiles. This mutagenesis-based study opens the field for further intermolecular bond-forming reactions and the generation of non-natural products. 相似文献
100.
CD4+ T cells orchestrate adaptive immune responses through their capacity to recruit and provide help to multiple immune effectors, in addition to exerting direct effector functions. CD4+ T cells are increasingly recognized as playing an essential role in the control of chronic viral infections. In this review, we present recent advances in understanding the nature of CD4+ T cell help provided to antiviral effectors. Drawing from our studies of natural human immunodeficiency virus (HIV) control, we then focus on the role of high-affinity T cell receptor (TCR) clonotypes in mediating antiviral CD4+ T cell responses. Last, we discuss the role of TCR affinity in determining CD4+ T cell differentiation, reviewing the at times divergent studies associating TCR signal strength to the choice of a T helper 1 (Th1) or a T follicular helper (Tfh) cell fate. 相似文献