全文获取类型
收费全文 | 6554篇 |
免费 | 530篇 |
国内免费 | 6篇 |
出版年
2023年 | 35篇 |
2022年 | 84篇 |
2021年 | 190篇 |
2020年 | 96篇 |
2019年 | 117篇 |
2018年 | 182篇 |
2017年 | 158篇 |
2016年 | 211篇 |
2015年 | 325篇 |
2014年 | 345篇 |
2013年 | 434篇 |
2012年 | 540篇 |
2011年 | 564篇 |
2010年 | 314篇 |
2009年 | 289篇 |
2008年 | 396篇 |
2007年 | 399篇 |
2006年 | 376篇 |
2005年 | 308篇 |
2004年 | 257篇 |
2003年 | 273篇 |
2002年 | 231篇 |
2001年 | 50篇 |
2000年 | 40篇 |
1999年 | 53篇 |
1998年 | 44篇 |
1997年 | 39篇 |
1996年 | 33篇 |
1995年 | 31篇 |
1994年 | 31篇 |
1993年 | 36篇 |
1992年 | 35篇 |
1991年 | 26篇 |
1990年 | 28篇 |
1989年 | 32篇 |
1988年 | 19篇 |
1987年 | 15篇 |
1986年 | 25篇 |
1985年 | 24篇 |
1984年 | 30篇 |
1983年 | 28篇 |
1982年 | 32篇 |
1981年 | 25篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1978年 | 23篇 |
1977年 | 21篇 |
1976年 | 22篇 |
1974年 | 18篇 |
1973年 | 13篇 |
排序方式: 共有7090条查询结果,搜索用时 15 毫秒
971.
The transthyretin-related protein family. 总被引:6,自引:0,他引:6
Therese Eneqvist Erik Lundberg Lars Nilsson Ruben Abagyan A Elisabeth Sauer-Eriksson 《European journal of biochemistry》2003,270(3):518-532
A number of proteins related to the homotetrameric transport protein transthyretin (TTR) forms a highly conserved protein family, which we present in an integrated analysis of data from different sources combined with an initial biochemical characterization. Homologues of the transthyretin-related protein (TRP) can be found in a wide range of species including bacteria, plants and animals, whereas transthyretins have so far only been identified in vertebrates. A multiple sequence alignment of 49 TRP sequences from 47 species to TTR suggests that the tertiary and quaternary features of the three-dimensional structure are most likely preserved. Interestingly, while some of the TRP orthologues show as little as 30% identity, the residues at the putative ligand-binding site are almost entirely conserved. RT/PCR analysis in Caenorhabditis elegans confirms that one TRP gene is transcribed, spliced and predominantly expressed in the worm, which suggests that at least one of the two C. elegans TRP genes encodes a functional protein. We used double-stranded RNA-mediated interference techniques in order to determine the loss-of-function phenotype for the two TRP genes in C. elegans but detected no apparent phenotype. The cloning and initial characterization of purified TRP from Escherichia coli reveals that, while still forming a homotetramer, this protein does not recognize thyroid hormones that are the natural ligands of TTR. The ligand for TRP is not known; however, genomic data support a functional role involving purine catabolism especially linked to urate oxidase (uricase) activity. 相似文献
972.
Hamid Pahlevaninezhad Anthony M. D. Lee Miriam Rosin Ivan Sun Lewei Zhang Mehrnoush Hakimi Calum MacAulay Pierre M. Lane 《PloS one》2014,9(12)
For the first time, we present co-registered autofluorescence imaging and optical coherence tomography (AF/OCT) of excised human palatine tonsils to evaluate the capabilities of OCT to visualize tonsil tissue components. Despite limited penetration depth, OCT can provide detailed structural information about tonsil tissue with much higher resolution than that of computed tomography, magnetic resonance imaging, and Ultrasound. Different tonsil tissue components such as epithelium, dense connective tissue, lymphoid nodules, and crypts can be visualized by OCT. The co-registered AF imaging can provide matching biochemical information. AF/OCT scans may provide a non-invasive tool for detecting tonsillar cancers and for studying the natural history of their development. 相似文献
973.
According to a general paradigm, proper DNA duplication from each replication origin is ensured by two protein complexes termed replisomes. In prokaryotes and in budding yeast Saccharomyces cerevisiae, these two replisomes seem to be associated with one another until DNA replication initiated from the origin has finished. This arrangement results in the formation of the loop of newly synthesized DNA. However, arrangement of replisomes in other eukaryotic organisms including vertebrate cells is largely unknown. Here, we used in vivo labeling of DNA segments in combination with the electron microscopy tomography to describe the organization of replisomes in human HeLa cells. The experiments were devised in order to distinguish between a model of independent replisomes and a model of replisome couples. The comparative analysis of short segments of replicons labeled in pulse-chase experiments of various length shows that replisomes in HeLa cells are organized into the couples during DNA replication. Moreover, our data enabled to suggest a new model of the organization of replicated DNA. According to this model, replisome couples produce loop with the associated arms in the form of four tightly associated 30 nm fibers. 相似文献
974.
Zhen Zheng Long Chang Ivan Nekrashevich Paul Ruchhoeft Sakhrat Khizroev Dmitri Litvinov 《PloS one》2013,8(8)
We describe a low-energy glow-discharge process using reactive ion etching system that enables non-circular device patterns, such as squares or hexagons, to be formed from a precursor array of uniform circular openings in polymethyl methacrylate, PMMA, defined by electron beam lithography. This technique is of a particular interest for bit-patterned magnetic recording medium fabrication, where close packed square magnetic bits may improve its recording performance. The process and results of generating close packed square patterns by self-limiting low-energy glow-discharge are investigated. Dense magnetic arrays formed by electrochemical deposition of nickel over self-limiting formed molds are demonstrated. 相似文献
975.
Katia C. Barbaro Marcelo V. Sousa Lauro Morhy Vera R. D. Eickstedt Ivan Mota 《Journal of Protein Chemistry》1996,15(4):337-343
Loxosceles spider venom usually causes a typical dermonecrotic lesion in bitten patients, but it may also cause systemic effects that may be lethal. Gel filtration on Sephadex G-100 ofLoxosceles gaucho, L. laeta, orL. intermedia spider venoms resulted in three fractions (A, containing higher molecular mass components, B containing intermediate molecular mass components, and C with lower molecular mass components). The dermonecrotic and lethal activities were detected exclusively in fraction A of all three species. Analysis by SDS-PAGE showed that the major protein contained in fraction A has molecular weight approximately 35 kDa inL. gaucho andL. intermedia, but 32 kDa inL. laeta venom. These toxins were isolated from venoms ofL. gaucho, L. laeta, andL. intermedia by SDS-PAGE followed by blotting to PVDF membrane and sequencing. A database search showed a high level of identity between each toxin and a fragment of theL. reclusa (North American spider) toxin. A multiple sequence alignment of theLoxosceles toxins showed many common identical residues in their N-terminal sequences. Identities ranged from 50.0% (L. gaucho andL. reclusa) to 61.1% (L. intermedia andL. reclusa). The purified toxins were also submitted to capillary electrophoresis peptide mapping afterin situ partial hydrolysis of the blotted samples. The results obtained suggest thatL. intermedia protein is more similar toL. laeta toxin thanL. gaucho toxin and revealed a smaller homology betweenL. intermedia andL gaucho. Altogether these findings suggest that the toxins responsible for most important activities of venoms ofLoxosceles species have a molecular mass of 32–35 kDa and are probably homologous proteins. 相似文献
976.
977.
Valentina Diehl Martin Wegner Paolo Grumati Koraljka Husnjak Simone Schaubeck Andrea Gubas Varun
Jayeshkumar Shah Ibrahim
H Polat Felix Langschied Cristian Prieto-Garcia Konstantin Müller Alkmini Kalousi Ingo Ebersberger Christian
H Brandts Ivan Dikic Manuel Kaulich 《Nucleic acids research》2021,49(10):5684
Combinatorial CRISPR-Cas screens have advanced the mapping of genetic interactions, but their experimental scale limits the number of targetable gene combinations. Here, we describe 3Cs multiplexing, a rapid and scalable method to generate highly diverse and uniformly distributed combinatorial CRISPR libraries. We demonstrate that the library distribution skew is the critical determinant of its required screening coverage. By circumventing iterative cloning of PCR-amplified oligonucleotides, 3Cs multiplexing facilitates the generation of combinatorial CRISPR libraries with low distribution skews. We show that combinatorial 3Cs libraries can be screened with minimal coverages, reducing associated efforts and costs at least 10-fold. We apply a 3Cs multiplexing library targeting 12,736 autophagy gene combinations with 247,032 paired gRNAs in viability and reporter-based enrichment screens. In the viability screen, we identify, among others, the synthetic lethal WDR45B-PIK3R4 and the proliferation-enhancing ATG7-KEAP1 genetic interactions. In the reporter-based screen, we identify over 1,570 essential genetic interactions for autophagy flux, including interactions among paralogous genes, namely ATG2A-ATG2B, GABARAP-MAP1LC3B and GABARAP-GABARAPL2. However, we only observe few genetic interactions within paralogous gene families of more than two members, indicating functional compensation between them. This work establishes 3Cs multiplexing as a platform for genetic interaction screens at scale. 相似文献
978.
Josef ?pak Ivan Votruba Daniela Pavingerová Antonín Holy Vlastimila ?paková Karel Petrzik 《Plant Cell, Tissue and Organ Culture》2012,110(1):63-68
Antiviral effects of acyclic nucleoside phosphonates PMEA, (S)-HPMPC, PMEDAP, and ribavirin on double-stranded DNA Cauliflower mosaic virus (CaMV) were evaluated in Brassica pekinensis plants grown in vitro on liquid medium. A double-antibody sandwich ELISA was used for relative quantification of viral protein and PCR for detection of CaMV nucleic acid in plants. Ribavirin and PMEA had no significant antiviral effect. (S)-HPMPC at concentration 50?mg?l?1 and PMEDAP at concentrations 50 and 12.5?mg?l?1 significantly (P?<?0.05) reduced CaMV concentration in plants within 42?C63?days to levels detectable neither by ELISA nor by PCR. A phytotoxicity experiment resulted in progressive yellowing of leaves and dwarfing in plants cultured 42?days on media with concentrations 12.5, 25 and 50?mg?l?1 of (S)-HPMPC and PMEDAP. Reduction in fresh and dry weights of plants was significant (P?<?0.05) already at 12.5?mg?l?1 with both compounds. 相似文献
979.
Ilia Fishbein Scott P. Forbes Richard F. Adamo Michael Chorny Robert J. Levy Ivan S. Alferiev 《Journal of visualized experiments : JoVE》2014,(90)
In-stent restenosis presents a major complication of stent-based revascularization procedures widely used to re-establish blood flow through critically narrowed segments of coronary and peripheral arteries. Endovascular stents capable of tunable release of genes with anti-restenotic activity may present an alternative strategy to presently used drug-eluting stents. In order to attain clinical translation, gene-eluting stents must exhibit predictable kinetics of stent-immobilized gene vector release and site-specific transduction of vasculature, while avoiding an excessive inflammatory response typically associated with the polymer coatings used for physical entrapment of the vector. This paper describes a detailed methodology for coatless tethering of adenoviral gene vectors to stents based on a reversible binding of the adenoviral particles to polyallylamine bisphosphonate (PABT)-modified stainless steel surface via hydrolysable cross-linkers (HC). A family of bifunctional (amine- and thiol-reactive) HC with an average t1/2 of the in-chain ester hydrolysis ranging between 5 and 50 days were used to link the vector with the stent. The vector immobilization procedure is typically carried out within 9 hr and consists of several steps: 1) incubation of the metal samples in an aqueous solution of PABT (4 hr); 2) deprotection of thiol groups installed in PABT with tris(2-carboxyethyl) phosphine (20 min); 3) expansion of thiol reactive capacity of the metal surface by reacting the samples with polyethyleneimine derivatized with pyridyldithio (PDT) groups (2 hr); 4) conversion of PDT groups to thiols with dithiothreitol (10 min); 5) modification of adenoviruses with HC (1 hr); 6) purification of modified adenoviral particles by size-exclusion column chromatography (15 min) and 7) immobilization of thiol-reactive adenoviral particles on the thiolated steel surface (1 hr). This technique has wide potential applicability beyond stents, by facilitating surface engineering of bioprosthetic devices to enhance their biocompatibility through the substrate-mediated gene delivery to the cells interfacing the implanted foreign material. 相似文献
980.