全文获取类型
收费全文 | 19538篇 |
免费 | 1768篇 |
国内免费 | 2187篇 |
专业分类
23493篇 |
出版年
2024年 | 56篇 |
2023年 | 289篇 |
2022年 | 611篇 |
2021年 | 992篇 |
2020年 | 720篇 |
2019年 | 864篇 |
2018年 | 897篇 |
2017年 | 602篇 |
2016年 | 813篇 |
2015年 | 1252篇 |
2014年 | 1530篇 |
2013年 | 1587篇 |
2012年 | 1908篇 |
2011年 | 1714篇 |
2010年 | 1105篇 |
2009年 | 1050篇 |
2008年 | 1128篇 |
2007年 | 1056篇 |
2006年 | 866篇 |
2005年 | 711篇 |
2004年 | 638篇 |
2003年 | 544篇 |
2002年 | 464篇 |
2001年 | 310篇 |
2000年 | 296篇 |
1999年 | 270篇 |
1998年 | 189篇 |
1997年 | 155篇 |
1996年 | 144篇 |
1995年 | 96篇 |
1994年 | 122篇 |
1993年 | 66篇 |
1992年 | 86篇 |
1991年 | 68篇 |
1990年 | 63篇 |
1989年 | 40篇 |
1988年 | 34篇 |
1987年 | 21篇 |
1986年 | 16篇 |
1985年 | 25篇 |
1984年 | 13篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1980年 | 4篇 |
1978年 | 5篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1968年 | 3篇 |
1965年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
Biftu T Feng D Ponpipom M Girotra N Liang GB Qian X Bugianesi R Simeone J Chang L Gurnett A Liberator P Dulski P Leavitt PS Crumley T Misura A Murphy T Rattray S Samaras S Tamas T Mathew J Brown C Thompson D Schmatz D Fisher M Wyvratt M 《Bioorganic & medicinal chemistry letters》2005,15(13):3296-3301
Several analogs of 2,3-diaryl pyrroles were synthesized and evaluated as inhibitors of Eimeria tenella cGMP-dependent protein kinase and in in vivo anticoccidial assays. A 4-fluorophenyl group enhances both in vitro and in vivo activities. The most potent analogs are the 5-(N-methyl, N-ethyl, and N-methylazetidine methyl) piperidyl derivatives 12, 23, and 34. These compounds have a broad spectrum of activity. Based on the in vivo efficacy and cost of synthesis, the N-ethyl analog 23 was chosen as a novel anticoccidial agent for a field trial. 相似文献
103.
Youshuang Zhu Haibo Zhang Mingle Cao Zhenzhen Wei Feng Huang Peiji Gao 《Biotechnology and Bioprocess Engineering》2011,16(5):1027-1035
Production of laccase using a submerged culture of Trametes versicolor sdu-4 was optimized using a central composite design of the Response Surface Methodology. Optimized conditions gave a laccase
yield of 4,213 U/L which was approximately three times of that in basal medium. The laccase was purified to homogeneity using
a three-step process. The overall yield of the purification was 58%, with a purification fold of 11.4 and a specific activity
of 1320.7 U/mg protein. The molecular mass of the laccase was 60 kDa. The optimum pH values of the enzyme were 2.2, 3.7, and
7 for the oxidations of ABTS, DMP, and syringaldazine, respectively. The enzyme had adaptability to a broad pH range and high
temperature and wsa stable at pH 3.0 ∼ 10.0. The half-life of this laccase at 70°C was 2.2 h. Methyl red, 2-bromophenol, and
4-bromophenol were oxidized by the purified laccase in the absence of mediators. Purified laccase was effective in the decolorization
of several dyes and was not inhibited by Cu2+, Mn2+, Zn2+, Na+, K+, Mg2+, Ba2+, and Ca2+ at 5 mM. These excellent characteristics made it a highly attractive candidate for industrial use. 相似文献
104.
105.
Donor–Acceptor–Acceptor's Molecules for Vacuum‐Deposited Organic Photovoltaics with Efficiency Exceeding 9% 下载免费PDF全文
Xiaozhou Che Chin‐Lung Chung Chou‐Chun Hsu Feng Liu Ken‐Tsung Wong Stephen R. Forrest 《Liver Transplantation》2018,8(19)
Three vacuum‐deposited donor–acceptor–acceptor (d–a–a') small molecule donors are studied with different side chains attached to an asymmetric heterotetracene donor block for use in high efficiency organic photovoltaics (OPVs). The donor with an isobutyl side chain yields the highest crystal packing density compared to molecules with 2‐ethylhexyl or n‐butyl chains, leading to the largest absorption coefficient and short circuit current in an OPV. It also exhibits a higher fill factor, consistent with its preferred out‐of‐plane molecular π–π stacking arrangement that facilitates charge transport in the direction perpendicular to the substrate. A power conversion efficiency of 9.3 ± 0.5% is achieved under 1 sun intensity, AM 1.5 G simulated solar illumination, which is significantly higher than 7.5 ± 0.4% of the other two molecules. These results indicate that side chain modification of d–a–a' small molecules offers an effective approach to control the crystal packing configuration, thereby improving the device performance. 相似文献
106.
CuS Microspheres with Tunable Interlayer Space and Micropore as a High‐Rate and Long‐Life Anode for Sodium‐Ion Batteries 下载免费PDF全文
Yuanhua Xiao Dangcheng Su Xuezhao Wang Shide Wu Liming Zhou Ying Shi Shaoming Fang Hui‐Ming Cheng Feng Li 《Liver Transplantation》2018,8(22)
Layered transition metal sulfides (LTMSs) have tremendous commercial potential in anode materials for sodium‐ion batteries (SIBs) in large‐scale energy storage application. However, it is a great challenge for most LTMS electrodes to have long cycling life and high‐rate capability due to their larger volume expansion and the formation of soluble polysulfide intermediates caused by the conversion reaction. Herein, layered CuS microspheres with tunable interlayer space and pore volumes are reported through a cost‐effective interaction method using a cationic surfactant of cetyltrimethyl ammonium bromide (CTAB). The CuS–CTAB microsphere as an anode for SIBs reveals a high reversible capacity of 684.6 mAh g?1 at 0.1 A g?1, and 312.5 mAh g?1 at 10 A g?1 after 1000 cycles with high capacity retention of 90.6%. The excellent electrochemical performance is attributed to the unique structure of this material, and a high pseudocapacitive contribution ensures its high‐rate performance. Moreover, in situ X‐ray diffraction is applied to investigate their sodium storage mechanism. It is found that the long chain CTAB in the CuS provides buffer space, traps polysulfides, and restrains the further growth of Cu particles during the conversion reaction process that ensure the long cycling stability and high reversibility of the electrode material. 相似文献
107.
Li NJ Zeng GM Huang DL Hu S Feng CL Zhao MH Lai C Huang C Wei Z Xie GX 《Bioresource technology》2011,102(17):8137-8142
The production of oxalate at different initial Pb2+ concentrations during solid-state fermentation of straw with Phanerochaete chrysosporium was investigated. It was found that the maximal peak value of oxalate concentration (22.84 mM) was detected at the initial Pb2+ concentration of 200 mg kg−1 dry straw, while the minimum (15.89 mM) at the concentration of 600 mg Pb2+ kg−1 dry straw, and at moderate concentration of Pb2+ the capability of oxalic acid secretion was enhanced. In addition, it was also found that more oxalic acid accumulation went together with better Pb2+ passivation effect and higher manganese peroxidase (MnP) activity. The present findings will improve the understandings of the interactions of heavy metals with white-rot fungi and the role of oxalate in lignin degradation system, which could provide useful references for more efficient treatment of Pb-contaminated lignocellulosic waste. 相似文献
108.
Winstone N Wilson AJ Morrow G Boggiano C Chiuchiolo MJ Lopez M Kemelman M Ginsberg AA Mullen K Coleman JW Wu CD Narpala S Ouellette I Dean HJ Lin F Sardesai NY Cassamasa H McBride D Felber BK Pavlakis GN Schultz A Hudgens MG King CR Zamb TJ Parks CL McDermott AB 《Journal of virology》2011,85(18):9578-9587
DNA priming has previously been shown to elicit augmented immune responses when administered by electroporation (EP) or codelivered with a plasmid encoding interleukin-12 (pIL-12). We hypothesized that the efficacy of a DNA prime and recombinant adenovirus 5 boost vaccination regimen (DNA/rAd5) would be improved when incorporating these vaccination strategies into the DNA priming phase, as determined by pathogenic simian immunodeficiency virus SIVmac239 challenge outcome. The whole SIVmac239 proteome was delivered in 5 separate DNA plasmids (pDNA-SIV) by EP with or without pIL-12, followed by boosting 4 months later with corresponding rAd5-SIV vaccine vectors. Remarkably, after repeated low-dose SIVmac239 mucosal challenge, we demonstrate 2.6 and 4.4 log reductions of the median SIV peak and set point viral loads in rhesus macaques (RMs) that received pDNA-SIV by EP with pIL-12 compared to the median peak and set point viral loads in mock-immunized controls (P < 0.01). In 5 out of 6 infected RMs, strong suppression of viremia was observed, with intermittent "blips" in virus replication. In 2 RMs, we could not detect the presence of SIV RNA in tissue and lymph nodes, even after 13 viral challenges. RMs immunized without pIL-12 demonstrated a typical maximum of 1.5 log reduction in virus load. There was no significant difference in the overall magnitude of SIV-specific antibodies or CD8 T-cell responses between groups; however, pDNA delivery by EP with pIL-12 induced a greater magnitude of SIV-specific CD4 T cells that produced multiple cytokines. This vaccine strategy is relevant for existing vaccine candidates entering clinical evaluation, and this model may provide insights into control of retrovirus replication. 相似文献
109.
110.
Dun Wang Xiao‐Fei Li Zheng‐Jian Zhou Xu‐Ping Feng Wan‐Jun Yang De‐An Jiang 《Physiologia plantarum》2010,139(1):55-67
Studies on some plant species have shown that increasing the growth temperature gradually or pretreating with high temperature can lead to obvious photosynthetic acclimation to high temperature. To test whether this acclimation arises from heat adaptation of ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) activation mediated by Rubisco activase (RCA), gene expression of RCA large isoform (RCAL) and RCA small isoform (RCAS) in rice was determined using a 4‐day heat stress treatment [40/30°C (day/night)] followed by a 3‐day recovery under control conditions [30/22°C (day/night)]. The heat stress significantly induced the expression of RCAL as determined by both mRNA and protein levels. Correlative analysis indicated that RCAS protein content was extremely significantly related to Rubisco initial activity and net photosynthetic rate (Pn) under both heat stress and normal conditions. Immunoblot analysis of the Rubisco–RCA complex revealed that the ratio of RCAL to Rubisco increased markedly in heat‐acclimated rice leaves. Furthermore, transgenic rice plants expressing enhanced amounts of RCAL exhibited higher thermotolerance in Pn and Rubisco initial activity and grew better at high temperature than wild‐type (WT) plants and transgenic rice plants expressing enhanced amounts of RCAS. Under normal conditions, the transgenic rice plants expressing enhanced amounts of RCAS showed higher Pn and produced more biomass than transgenic rice plants expressing enhanced amounts of RCAL and wild‐type plants. Together, these suggest that the heat‐induced RCAL may play an important role in photosynthetic acclimation to moderate heat stress in vivo, while RCAS plays a major role in maintaining Rubisco initial activity under normal conditions. 相似文献