全文获取类型
收费全文 | 1469篇 |
免费 | 229篇 |
出版年
2021年 | 31篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 16篇 |
2017年 | 12篇 |
2016年 | 25篇 |
2015年 | 37篇 |
2014年 | 38篇 |
2013年 | 78篇 |
2012年 | 56篇 |
2011年 | 59篇 |
2010年 | 43篇 |
2009年 | 35篇 |
2008年 | 50篇 |
2007年 | 56篇 |
2006年 | 49篇 |
2005年 | 52篇 |
2004年 | 62篇 |
2003年 | 52篇 |
2002年 | 44篇 |
2001年 | 48篇 |
2000年 | 56篇 |
1999年 | 42篇 |
1998年 | 19篇 |
1997年 | 18篇 |
1996年 | 20篇 |
1995年 | 12篇 |
1994年 | 17篇 |
1993年 | 18篇 |
1992年 | 35篇 |
1991年 | 47篇 |
1990年 | 47篇 |
1989年 | 28篇 |
1988年 | 37篇 |
1987年 | 28篇 |
1986年 | 30篇 |
1985年 | 28篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 21篇 |
1981年 | 14篇 |
1979年 | 14篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 17篇 |
1975年 | 16篇 |
1974年 | 17篇 |
1973年 | 19篇 |
1970年 | 23篇 |
1968年 | 18篇 |
排序方式: 共有1698条查询结果,搜索用时 31 毫秒
91.
Cross Adam T. Stevens Jason C. Sadler Rohan Moreira-Grez Benjamin Ivanov Dmitry Zhong Hongtao Dixon Kingsley W. Lambers Hans 《Plant and Soil》2021,460(1-2):163-176
Plant and Soil - In water-limited areas, shrubs influence biological soil crust (biocrust) composition and diversity via soil microenvironment alterations and through modifying biotic interactions... 相似文献
92.
93.
94.
95.
Paul W. Finch Lawrence J. Mark Cross Daniel F. McAuley Catherine L. Farrell 《Journal of cellular and molecular medicine》2013,17(9):1065-1087
Keratinocyte growth factor (KGF) is a paracrine‐acting epithelial mitogen produced by cells of mesenchymal origin, that plays an important role in protecting and repairing epithelial tissues. Pre‐clinical data initially demonstrated that a recombinant truncated KGF (palifermin) could reduce gastrointestinal injury and mortality resulting from a variety of toxic exposures. Furthermore, the use of palifermin in patients with hematological malignancies reduced the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. Based upon these findings, as well as the observation that KGF receptors are expressed in many, if not all, epithelial tissues, pre‐clinical studies have been conducted to determine the efficacy of palifermin in protecting different epithelial tissues from toxic injury in an attempt to model various clinical situations in which it might prove to be of benefit in limiting tissue damage. In this article, we review these studies to provide the pre‐clinical background for clinical trials that are described in the accompanying article and the rationale for additional clinical applications of palifermin. 相似文献
96.
Mary C. Chang Albert J. Cross Graham R. Fleming 《Journal of biomolecular structure & dynamics》2013,31(1):299-318
Abstract Time-resolved fluorescence depolarization on the nanosecond and sub-nanosecond time scales is a powerful technique for the study of rapid motions in the condensed phase. We apply this technique to measure the motions of proteins using both extrinsic and intrinsic probes. Eosin, which absorbs and fluoresces in the visible, forms a one-to-one complex with lysozyme binding in the hydrophobic box region and is used as an extrinsic probe of lysozyme motion. The long-time anisotropy of bound eosin is used to measure the overall rotation time of lysozyme for which refined values are presented. In addition, our measurements show a rapid restricted motion of the eosin molecule on the time scale of ~ 100 ps. The order parameter, a model independent measure of the extent of the restriction of the rapid motions, decreases with increasing temperature, indicating that the motion of the eosin is less hindered as temperature increases. We compare our results with the crystallographic measurements of least square displacements for the hydrophobic box region. Our measurements provide direct time resolved confirmation that the displacements observed in this region correspond to rapid motion. 相似文献
97.
V KW Wong T Li B YK Law E DL Ma N C Yip F Michelangeli C KM Law M M Zhang K YC Lam P L Chan L Liu 《Cell death & disease》2013,4(7):e720
Autophagy is an important cellular process that controls cells in a normal homeostatic state by recycling nutrients to maintain cellular energy levels for cell survival via the turnover of proteins and damaged organelles. However, persistent activation of autophagy can lead to excessive depletion of cellular organelles and essential proteins, leading to caspase-independent autophagic cell death. As such, inducing cell death through this autophagic mechanism could be an alternative approach to the treatment of cancers. Recently, we have identified a novel autophagic inducer, saikosaponin-d (Ssd), from a medicinal plant that induces autophagy in various types of cancer cells through the formation of autophagosomes as measured by GFP-LC3 puncta formation. By computational virtual docking analysis, biochemical assays and advanced live-cell imaging techniques, Ssd was shown to increase cytosolic calcium level via direct inhibition of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase pump, leading to autophagy induction through the activation of the Ca2+/calmodulin-dependent kinase kinase–AMP-activated protein kinase–mammalian target of rapamycin pathway. In addition, Ssd treatment causes the disruption of calcium homeostasis, which induces endoplasmic reticulum stress as well as the unfolded protein responses pathway. Ssd also proved to be a potent cytotoxic agent in apoptosis-defective or apoptosis-resistant mouse embryonic fibroblast cells, which either lack caspases 3, 7 or 8 or had the Bax-Bak double knockout. These results provide a detailed understanding of the mechanism of action of Ssd, as a novel autophagic inducer, which has the potential of being developed into an anti-cancer agent for targeting apoptosis-resistant cancer cells. 相似文献
98.
Chad K. Bush Dayaamayi Kurimella Lee J. S. Cross Katherine R. Conner Sheryl Martin-Schild Jiang He Changwei Li Jing Chen Tanika Kelly 《PloS one》2016,11(1)
Importance
Acute ischemic stroke is a leading cause of death and disability worldwide. Several recent clinical trials have shown that endovascular treatment improves clinical outcomes among patients with acute ischemic stroke.Objective
To provide an overall and precise estimate of the efficacy of endovascular treatment predominantly using second-generation mechanical thrombectomy devices (stent-retriever devices) compared to medical management on clinical and functional outcomes among patients with acute ischemic stroke.Data Sources
MEDLINE, EMBASE, Cochrane Collaboration Central Register of Controlled Clinical Trials, Web of Science, and NIH ClinicalTrials.gov were searched through November 2015.Study Selection
Searches returned 3,045 articles. After removal of duplicates, two authors independently screened titles and abstracts to assess eligibility of 2,495 potentially relevant publications. From these, 38 full-text publications were more closely assessed. Finally, 5 randomized controlled trials of endovascular treatment with predominant use of retrievable stents were selected.Data Extraction and Synthesis
Three authors independently extracted information on participant and trial characteristics and clinical events using a standardized protocol. Random effects models were used to pool endovascular treatment effects across outcomes.Main Outcomes and Measures
The primary outcome was better functional outcome as measured on the modified Rankin Scale at 90 days of follow-up. Secondary outcomes included all-cause mortality and symptomatic intra-cerebral hemorrhage.Results
Five trials representing 1,287 patients were included. Overall, patients randomized to endovascular therapy experienced 2.22 times greater odds of better functional outcome compared to those randomized to medical management (95% CI, 1.66 to 2.98; P < 0.0001). Endovascular therapy was not associated with mortality [OR (95% CI), 0.78 (0.54, 1.12); P = 0.1056] or symptomatic intracerebral hemorrhage [OR (95% CI), 1.19 (0.69, 2.05); P = 0.5348]. Meta-regression analysis suggested that shorter times from stroke onset to groin puncture and from stroke onset to reperfusion result in better functional outcomes in ischemic stroke patients (P = 0.0077 and P = 0.0089). There were no significant differences in the beneficial effects of endovascular treatment on functional outcomes across categories of gender, age, stroke severity, ischemic changes on computed tomography, or intravenous tissue plasminogen activator administration.Conclusions and Relevance
This meta-analysis demonstrated superior functional outcomes in subjects receiving endovascular treatment compared to medical management. Further, this analysis showed that acute ischemic stroke patients may receive enhanced functional benefit from earlier endovascular treatment. 相似文献99.
Seed reproductive biology of the rare aquatic carnivorous plant Aldrovanda vesiculosa (Droseraceae) 下载免费PDF全文
Adam T. Cross Lubomír Adamec Shane R. Turner Kingsley W. Dixon David J. Merritt 《Botanical journal of the Linnean Society. Linnean Society of London》2016,180(4):515-529
Despite the unprecedented global decline in extant populations of Aldrovanda vesiculosa in the last century, little is known about the reproductive biology of this iconic aquatic carnivorous plant. This study aimed to investigate the role of seed‐based reproduction in the ecology of A. vesiculosa, with particular focus on the interplay between the regulation of seed dormancy by temperature cues and the efficacy of exogenous ethylene gas to act as a germination stimulant, the desiccation capacity and long‐term storage potential of seeds for conservation purposes. Sexual reproduction appears to be extremely limited in both natural and naturalized populations across three continents, with high variability in the success of flowering and seed set between sites and between seasons. Overall, flowering yielded few fertile fruit (6–19% of flowers producing fertile fruit) and seed viability was variable but generally low (29–88%). Fecundity appears to be influenced by seasonal climatic conditions and microhabitat characteristics. Aldrovanda vesiculosa possesses physiologically dormant seeds, with germination stimulated by exposure to ethylene gas (>90% germination) at 25 °C. Seeds appear sensitive to desiccation and sub‐zero temperature storage, with no germination and markedly reduced embryo growth after storage of seeds for >1 month at 15 °C and 15% relative humidity or after short‐term (24 h) storage at ?18 °C. In the absence of significant conservation and restoration initiatives, the continuing decline of dystrophic freshwater wetland habitats globally leaves A. vesiculosa facing extinction. As the successful long‐term storage of seeds appears unfeasible based on the approaches described in this study, other alternatives for germplasm conservation such as cryostorage of vegetative tissues or zygotic embryos must be considered for establishing long‐term ex situ collections of critical germplasm. 相似文献
100.
Kezia R. Manlove Josephine G. Walker Meggan E. Craft Kathryn P. Huyvaert Maxwell B. Joseph Ryan S. Miller Pauline Nol Kelly A. Patyk Daniel O’Brien Daniel P. Walsh Paul C. Cross 《PLoS biology》2016,14(4)
The One Health initiative is a global effort fostering interdisciplinary collaborations to address challenges in human, animal, and environmental health. While One Health has received considerable press, its benefits remain unclear because its effects have not been quantitatively described. We systematically surveyed the published literature and used social network analysis to measure interdisciplinarity in One Health studies constructing dynamic pathogen transmission models. The number of publications fulfilling our search criteria increased by 14.6% per year, which is faster than growth rates for life sciences as a whole and for most biology subdisciplines. Surveyed publications clustered into three communities: one used by ecologists, one used by veterinarians, and a third diverse-authorship community used by population biologists, mathematicians, epidemiologists, and experts in human health. Overlap between these communities increased through time in terms of author number, diversity of co-author affiliations, and diversity of citations. However, communities continue to differ in the systems studied, questions asked, and methods employed. While the infectious disease research community has made significant progress toward integrating its participating disciplines, some segregation—especially along the veterinary/ecological research interface—remains. 相似文献