全文获取类型
收费全文 | 18295篇 |
免费 | 1505篇 |
国内免费 | 1篇 |
出版年
2023年 | 56篇 |
2022年 | 40篇 |
2021年 | 207篇 |
2020年 | 174篇 |
2019年 | 231篇 |
2018年 | 317篇 |
2017年 | 282篇 |
2016年 | 401篇 |
2015年 | 793篇 |
2014年 | 845篇 |
2013年 | 1067篇 |
2012年 | 1488篇 |
2011年 | 1459篇 |
2010年 | 877篇 |
2009年 | 866篇 |
2008年 | 1206篇 |
2007年 | 1219篇 |
2006年 | 1121篇 |
2005年 | 1128篇 |
2004年 | 990篇 |
2003年 | 931篇 |
2002年 | 908篇 |
2001年 | 202篇 |
2000年 | 154篇 |
1999年 | 187篇 |
1998年 | 261篇 |
1997年 | 149篇 |
1996年 | 127篇 |
1995年 | 143篇 |
1994年 | 127篇 |
1993年 | 119篇 |
1992年 | 105篇 |
1991年 | 86篇 |
1990年 | 94篇 |
1989年 | 90篇 |
1988年 | 82篇 |
1987年 | 60篇 |
1986年 | 75篇 |
1985年 | 77篇 |
1984年 | 98篇 |
1983年 | 75篇 |
1982年 | 88篇 |
1981年 | 106篇 |
1980年 | 88篇 |
1979年 | 61篇 |
1978年 | 68篇 |
1977年 | 55篇 |
1976年 | 40篇 |
1975年 | 39篇 |
1974年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Robert Fitzgerald Breann DeSantiago Danielle Y. Lee Guangdong Yang Jae Yeon Kim D. Brian Foster Yee Chan-Li Maureen R. Horton Reynold A. Panettieri Rui Wang Steven S. An 《Biochemical and biophysical research communications》2014
Here we explored the impact of hydrogen sulfide (H2S) on biophysical properties of the primary human airway smooth muscle (ASM)–the end effector of acute airway narrowing in asthma. Using magnetic twisting cytometry (MTC), we measured dynamic changes in the stiffness of isolated ASM, at the single-cell level, in response to varying doses of GYY4137 (1–10 mM). GYY4137 slowly released appreciable levels of H2S in the range of 10–275 μM, and H2S released was long lived. In isolated human ASM cells, GYY4137 acutely decreased stiffness (i.e. an indicator of the single-cell relaxation) in a dose-dependent fashion, and stiffness decreases were sustained in culture for 24 h. Human ASM cells showed protein expressions of cystathionine-γ-lyase (CSE; a H2S synthesizing enzyme) and ATP-sensitive potassium (KATP) channels. The KATP channel opener pinacidil effectively relaxed isolated ASM cells. In addition, pinacidil-induced ASM relaxation was completely inhibited by the treatment of cells with the KATP channel blocker glibenclamide. Glibenclamide also markedly attenuated GYY4137-mediated relaxation of isolated human ASM cells. Taken together, our findings demonstrate that H2S causes the relaxation of human ASM and implicate as well the role for sarcolemmal KATP channels. Finally, given that ASM cells express intrinsic enzymatic machinery of generating H2S, we suggest thereby this class of gasotransmitter can be further exploited for potential therapy against obstructive lung disease. 相似文献
3.
Ellen L. Kenchington Brian S. Nakashima Christopher T. Taggart Lorraine C. Hamilton 《PloS one》2015,10(3)
Capelin (Mallotus villosus) is a commercially exploited, key forage-fish species found in the boreal waters of the North Pacific and North Atlantic Oceans. We examined the population structure of capelin throughout their range in the Canadian northwest Atlantic Ocean using genetic-based methods. Capelin collected at ten beach and five demersal spawning locations over the period 2002 through 2008 (N = 3,433 fish) were genotyped using six polymorphic microsatellite loci. Temporally distinct samples were identified at three beach spawning locations: Chance Cove, Little Lawn and Straitsview, Newfoundland. Four capelin stocks are assumed for fisheries management in the northwest Atlantic Ocean based on meristics, morphometrics, tag returns, and seasonal distribution patterns. Our results suggested groupings that were somewhat different than the assumed structure, and indicate at least seven genetically defined populations arising from two ancestral populations. The spatial mosaic of capelin from each of the two basal cluster groups explains much of the observed geographic variability amongst neighbouring samples. The genetic-defined populations were resolved at Jost’s D
est ≥ 0.01 and were composed of fish collected 1) in the Gulf of St. Lawrence, 2) along the south and east coasts of Newfoundland, 3) along coastal northern Newfoundland and southern Labrador, 4) along coastal northern Labrador, 5) near the Saguenay River, and at two nearshore demersal spawning sites, 6) one at Grebes Nest off Bellevue Beach on the east coast of Newfoundland, and 7) one off the coast of Labrador at Domino Run. Moreover, the offshore demersal spawners on the Scotian Shelf and Southeast Shoal appeared to be related to the inshore demersal spawners at Grebes Nest and in Domino Run and to beach spawners from the Gulf of St. Lawrence. 相似文献
4.
The effect of hydrogen sulfide (H2S) on differentiation of 3T3L1-derived adipocytes was examined. Endogenous H2S was increased after 3T3L1 differentiation. The expression of the H2S-synthesising enzymes, cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST), was increased in a time-dependent manner during 3T3L1 differentiation. Expression of genes associated with adipogenesis related genes including fatty acid binding protein 4 (FABP4/aP2), a key regulator of this process, was increased by GYY4137 (a slow-releasing H2S donor compound) and sodium hydrosulfide (NaHS, a classical H2S donor) but not by ZYJ1122 or time-expired NaHS. Furthermore expression of these genes were reduced by aminooxyacetic acid (AOAA, CBS inhibitor), DL-propargylglycine (PAG, CSE inhibitor) as well as by CSE small interference RNA (siCSE) and siCBS. The size and number of lipid droplets in mature adipocytes was significantly increased by both GYY4137 and NaHS, which also impaired the ability of CL316,243 (β3-agonist) to promote lipolysis in these cells. In contrast, AOAA and PAG had the opposite effect. Taken together, we show that the H2S-synthesising enzymes CBS, CSE and 3-MST are endogenously expressed during adipogenesis and that both endogenous and exogenous H2S modulate adipogenesis and adipocyte maturation. 相似文献
5.
Objective assessment of changes in physical activity and sedentary behavior: Pre‐ through 3 years post‐bariatric surgery 下载免费PDF全文
6.
Light Oxygen Voltage (LOV) proteins are widely used in optogenetic devices, however universal signal transduction pathways and photocycle mechanisms remain elusive. In particular, short-LOV (sLOV) proteins have been discovered in bacteria and fungi, containing only the photoresponsive LOV element without any obvious signal transduction domains. These sLOV proteins may be ideal models for LOV domain function due to their ease of study as full-length proteins. Unfortunately, characterization of such proteins remains limited to select systems. Herein, we identify a family of bacterial sLOV proteins present in Methylocystis. Sequence analysis of Methylocystis LOV proteins (McLOV) demonstrates conservation with sLOV proteins from fungal systems that employ competitive dimerization as a signaling mechanism. Cloning and characterization of McLOV proteins confirms functional dimer formation and reveal unexpected photocycle mechanisms. Specifically, some McLOV photocycles are insensitive to external bases such as imidazole, in contrast to previously characterized LOV proteins. Mutational analysis identifies a key residue that imparts insensitivity to imidazole in two McLOV homologs and affects adduct decay by two orders of magnitude. The resultant data identifies a new family of LOV proteins that indicate a universal photocycle mechanism may not be present in LOV proteins. 相似文献
7.
Aruna S. Jaiswal Harekrushna Panda Brian K. Law Jay Sharma Jitesh Jani Robert Hromas Satya Narayan 《PloS one》2015,10(5)
Recently approved chemotherapeutic agents to treat colorectal cancer (CRC) have made some impact; however, there is an urgent need for newer targeted agents and strategies to circumvent CRC growth and metastasis. CRC frequently exhibits natural resistance to chemotherapy and those who do respond initially later acquire drug resistance. A mechanism to potentially sensitize CRC cells is by blocking the DNA polymerase β (Pol-β) activity. Temozolomide (TMZ), an alkylating agent, and other DNA-interacting agents exert DNA damage primarily repaired by a Pol-β-directed base excision repair (BER) pathway. In previous studies, we used structure-based molecular docking of Pol-β and identified a potent small molecule inhibitor (NSC666715). In the present study, we have determined the mechanism by which NSC666715 and its analogs block Fen1-induced strand-displacement activity of Pol-β-directed LP-BER, cause apurinic/apyrimidinic (AP) site accumulation and induce S-phase cell cycle arrest. Induction of S-phase cell cycle arrest leads to senescence and apoptosis of CRC cells through the p53/p21 pathway. Our initial findings also show a 10-fold reduction of the IC50 of TMZ when combined with NSC666715. These results provide a guide for the development of a target-defined strategy for CRC chemotherapy that will be based on the mechanisms of action of NSC666715 and TMZ. This combination strategy can be used as a framework to further reduce the TMZ dosages and resistance in CRC patients. 相似文献
8.
Global gene expression analysis using microarrays and, more recently, RNA-seq, has allowed investigators to understand biological processes at a system level. However, the identification of differentially expressed genes in experiments with small sample size, high dimensionality, and high variance remains challenging, limiting the usability of these tens of thousands of publicly available, and possibly many more unpublished, gene expression datasets. We propose a novel variable selection algorithm for ultra-low-n microarray studies using generalized linear model-based variable selection with a penalized binomial regression algorithm called penalized Euclidean distance (PED). Our method uses PED to build a classifier on the experimental data to rank genes by importance. In place of cross-validation, which is required by most similar methods but not reliable for experiments with small sample size, we use a simulation-based approach to additively build a list of differentially expressed genes from the rank-ordered list. Our simulation-based approach maintains a low false discovery rate while maximizing the number of differentially expressed genes identified, a feature critical for downstream pathway analysis. We apply our method to microarray data from an experiment perturbing the Notch signaling pathway in Xenopus laevis embryos. This dataset was chosen because it showed very little differential expression according to limma, a powerful and widely-used method for microarray analysis. Our method was able to detect a significant number of differentially expressed genes in this dataset and suggest future directions for investigation. Our method is easily adaptable for analysis of data from RNA-seq and other global expression experiments with low sample size and high dimensionality. 相似文献
9.
Ryan P. Goff Brian T. Howard Stephen G. Quallich Tinen L. Iles Paul A. Iaizzo 《BMC physiology》2015,16(1):4
Background
In vitro isolated heart preparations are valuable tools for the study of cardiac anatomy and physiology, as well as for preclinical device testing. Such preparations afford investigators a high level of hemodynamic control, independent of host or systemic interactions. Here we hypothesize that recovered human and swine heart-lung blocs can be reanimated using a clear perfusate and elicit viable cardiodynamic and pulmonic function. Further, this approach will facilitate multimodal imaging, which is particularly valuable for the study of both functional anatomy and device-tissue interactions. Five human and 18 swine heart-lung preparations were procured using techniques analogous to those for cardiac transplant. Specimens were then rewarmed and reperfused using modifications of a closed circuit, isolated, beating and ventilated heart-lung preparation. Positive pressure mechanical ventilation was also employed, and epicardial defibrillation was applied to elicit native cardiac sinus rhythm. Videoscopy, fluoroscopy, ultrasound, and infrared imaging were performed for anatomical and experimental study.Results
Systolic and diastolic left ventricular pressures observed for human and swine specimens were 68/2?±?11/7 and 74/3?±?17/5 mmHg, respectively, with associated native heart rates of 80?±?7 and 96?±?16 beats per minute. High-resolution imaging within functioning human pulmonary vasculature was obtained among other anatomies of interest. Note that one human specimen elicited poor cardiac performance post defibrillation.Conclusions
We report the first dynamic videoscopic images of the pulmonary vasculature during viable cardiopulmonary function in isolated reanimated heart-lung blocs. This experimental approach provides unique in vitro opportunities for the study of novel medical therapeutics applied to large mammalian, including human, heart-lung specimens.10.
Michael R. Kierny Thomas D. Cunningham Rachida A. Bouhenni Deepak P. Edward Brian K. Kay 《PloS one》2015,10(4)
Candidate biomarkers, indicative of disease or injury, are beginning to overwhelm the process of validation through immunological means. Recombinant antibodies developed through phage-display offer an alternative means of generating monoclonal antibodies faster than traditional immunization of animals. Peptide segments of putative biomarkers of laser induced injury in the rabbit, discovered through mass spectrometry, were used as targets for a selection against a library of phage-displayed human single-chain variable fragment (scFv) antibodies. Highly specific antibodies were isolated to four of these unique peptide sequences. One antibody against the retinal protein, Guanine Nucleotide-Binding Protein Beta 5 (GBB5), had a dissociation constant ~300 nM and recognized the full-length endogenous protein in retinal homogenates of three different animal species by western blot. Alanine scanning of the peptide target identified three charged and one hydrophobic amino acid as the critical binding residues for two different scFvs. To enhance the utility of the reagent, one scFv was dimerized through a Fragment-crystallizable hinge region (i.e., Fc) and expressed in HEK-293 cells. This dimeric reagent yielded a 25-fold lower detection limit in western blots. 相似文献