全文获取类型
收费全文 | 76334篇 |
免费 | 6613篇 |
国内免费 | 37篇 |
出版年
2021年 | 814篇 |
2020年 | 572篇 |
2019年 | 723篇 |
2018年 | 930篇 |
2017年 | 875篇 |
2016年 | 1457篇 |
2015年 | 2406篇 |
2014年 | 2744篇 |
2013年 | 3771篇 |
2012年 | 4622篇 |
2011年 | 4775篇 |
2010年 | 3144篇 |
2009年 | 2837篇 |
2008年 | 4206篇 |
2007年 | 4326篇 |
2006年 | 4143篇 |
2005年 | 4104篇 |
2004年 | 4198篇 |
2003年 | 3785篇 |
2002年 | 3792篇 |
2001年 | 876篇 |
2000年 | 618篇 |
1999年 | 841篇 |
1998年 | 1111篇 |
1997年 | 766篇 |
1996年 | 709篇 |
1995年 | 757篇 |
1994年 | 740篇 |
1993年 | 687篇 |
1992年 | 623篇 |
1991年 | 603篇 |
1990年 | 583篇 |
1989年 | 622篇 |
1988年 | 530篇 |
1987年 | 513篇 |
1986年 | 461篇 |
1985年 | 599篇 |
1984年 | 748篇 |
1983年 | 640篇 |
1982年 | 760篇 |
1981年 | 795篇 |
1980年 | 725篇 |
1979年 | 503篇 |
1978年 | 558篇 |
1977年 | 528篇 |
1976年 | 529篇 |
1975年 | 407篇 |
1974年 | 504篇 |
1973年 | 459篇 |
1970年 | 287篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
73.
74.
75.
The possible contribution of Na+-Ca2+ exchange to the triggering of Ca2+ release from the sarcoplasmic reticulum in ventricular cells remains unresolved. To gain insight into this issue, we measured the “trigger flux” of Ca2+ crossing the cell membrane in rabbit ventricular myocytes with Ca2+ release disabled pharmacologically. Under conditions that promote Ca2+ entry via Na+-Ca2+ exchange, internal [Na+] (10 mM), and positive membrane potential, the Ca2+ trigger flux (measured using a fluorescent Ca2+ indicator) was much greater than the Ca2+ flux through the L-type Ca2+ channel, indicating a significant contribution from Na+-Ca2+ exchange to the trigger flux. The difference between total trigger flux and flux through L-type Ca2+ channels was assessed by whole-cell patch-clamp recordings of Ca2+ current and complementary experiments in which internal [Na+] was reduced. However, Ca2+ entry via Na+-Ca2+ exchange measured in the absence of L-type Ca2+ current was considerably smaller than the amount inferred from the trigger flux measurements. From these results, we surmise that openings of L-type Ca2+ channels increase [Ca2+] near Na+-Ca2+ exchanger molecules and activate this protein. These results help to resolve seemingly contradictory results obtained previously and have implications for our understanding of the triggering of Ca2+ release in heart cells under various conditions. 相似文献
76.
77.
Shira Weingarten-Gabbay Susan Klaeger Siranush Sarkizova Leah R. Pearlman Da-Yuan Chen Kathleen M.E. Gallagher Matthew R. Bauer Hannah B. Taylor W. Augustine Dunn Christina Tarr John Sidney Suzanna Rachimi Hasahn L. Conway Katelin Katsis Yuntong Wang Del Leistritz-Edwards Melissa R. Durkin Christopher H. Tomkins-Tinch Pardis C. Sabeti 《Cell》2021,184(15):3962-3980.e17
78.
Neil E. Klepeis Suzanne C. Hughes Rufus D. Edwards Tracy Allen Michael Johnson Zohir Chowdhury Kirk R. Smith Marie Boman-Davis John Bellettiere Melbourne F. Hovell 《PloS one》2013,8(8)
Interventions are needed to protect the health of children who live with smokers. We pilot-tested a real-time intervention for promoting behavior change in homes that reduces second hand tobacco smoke (SHS) levels. The intervention uses a monitor and feedback system to provide immediate auditory and visual signals triggered at defined thresholds of fine particle concentration. Dynamic graphs of real-time particle levels are also shown on a computer screen. We experimentally evaluated the system, field-tested it in homes with smokers, and conducted focus groups to obtain general opinions. Laboratory tests of the monitor demonstrated SHS sensitivity, stability, precision equivalent to at least 1 µg/m3, and low noise. A linear relationship (R2 = 0.98) was observed between the monitor and average SHS mass concentrations up to 150 µg/m3. Focus groups and interviews with intervention participants showed in-home use to be acceptable and feasible. The intervention was evaluated in 3 homes with combined baseline and intervention periods lasting 9 to 15 full days. Two families modified their behavior by opening windows or doors, smoking outdoors, or smoking less. We observed evidence of lower SHS levels in these homes. The remaining household voiced reluctance to changing their smoking activity and did not exhibit lower SHS levels in main smoking areas or clear behavior change; however, family members expressed receptivity to smoking outdoors. This study established the feasibility of the real-time intervention, laying the groundwork for controlled trials with larger sample sizes. Visual and auditory cues may prompt family members to take immediate action to reduce SHS levels. Dynamic graphs of SHS levels may help families make decisions about specific mitigation approaches. 相似文献
79.
80.
John M. Szymanski Quentin Jallerat Adam W. Feinberg 《Journal of visualized experiments : JoVE》2014,(86)
The extracellular matrix (ECM) in tissues is synthesized and assembled by cells to form a 3D fibrillar, protein network with tightly regulated fiber diameter, composition and organization. In addition to providing structural support, the physical and chemical properties of the ECM play an important role in multiple cellular processes including adhesion, differentiation, and apoptosis. In vivo, the ECM is assembled by exposing cryptic self-assembly (fibrillogenesis) sites within proteins. This process varies for different proteins, but fibronectin (FN) fibrillogenesis is well-characterized and serves as a model system for cell-mediated ECM assembly. Specifically, cells use integrin receptors on the cell membrane to bind FN dimers and actomyosin-generated contractile forces to unfold and expose binding sites for assembly into insoluble fibers. This receptor-mediated process enables cells to assemble and organize the ECM from the cellular to tissue scales. Here, we present a method termed surface-initiated assembly (SIA), which recapitulates cell-mediated matrix assembly using protein-surface interactions to unfold ECM proteins and assemble them into insoluble fibers. First, ECM proteins are adsorbed onto a hydrophobic polydimethylsiloxane (PDMS) surface where they partially denature (unfold) and expose cryptic binding domains. The unfolded proteins are then transferred in well-defined micro- and nanopatterns through microcontact printing onto a thermally responsive poly(N-isopropylacrylamide) (PIPAAm) surface. Thermally-triggered dissolution of the PIPAAm leads to final assembly and release of insoluble ECM protein nanofibers and nanostructures with well-defined geometries. Complex architectures are possible by engineering defined patterns on the PDMS stamps used for microcontact printing. In addition to FN, the SIA process can be used with laminin, fibrinogen and collagens type I and IV to create multi-component ECM nanostructures. Thus, SIA can be used to engineer ECM protein-based materials with precise control over the protein composition, fiber geometry and scaffold architecture in order to recapitulate the structure and composition of the ECM in vivo. 相似文献