全文获取类型
收费全文 | 11022篇 |
免费 | 860篇 |
国内免费 | 8篇 |
专业分类
11890篇 |
出版年
2022年 | 59篇 |
2021年 | 97篇 |
2020年 | 52篇 |
2019年 | 88篇 |
2018年 | 130篇 |
2017年 | 145篇 |
2016年 | 197篇 |
2015年 | 349篇 |
2014年 | 378篇 |
2013年 | 516篇 |
2012年 | 619篇 |
2011年 | 648篇 |
2010年 | 437篇 |
2009年 | 435篇 |
2008年 | 578篇 |
2007年 | 663篇 |
2006年 | 629篇 |
2005年 | 630篇 |
2004年 | 609篇 |
2003年 | 610篇 |
2002年 | 618篇 |
2001年 | 140篇 |
2000年 | 134篇 |
1999年 | 174篇 |
1998年 | 215篇 |
1997年 | 162篇 |
1996年 | 143篇 |
1995年 | 141篇 |
1994年 | 131篇 |
1993年 | 154篇 |
1992年 | 177篇 |
1991年 | 133篇 |
1990年 | 146篇 |
1989年 | 117篇 |
1988年 | 99篇 |
1987年 | 93篇 |
1986年 | 73篇 |
1985年 | 114篇 |
1984年 | 102篇 |
1983年 | 78篇 |
1982年 | 97篇 |
1981年 | 84篇 |
1980年 | 76篇 |
1979年 | 75篇 |
1978年 | 61篇 |
1977年 | 75篇 |
1976年 | 69篇 |
1975年 | 46篇 |
1974年 | 46篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Seasonal encoding by the circadian pacemaker of the SCN 总被引:1,自引:0,他引:1
VanderLeest HT Houben T Michel S Deboer T Albus H Vansteensel MJ Block GD Meijer JH 《Current biology : CB》2007,17(5):468-473
The circadian pacemaker of the suprachiasmatic nucleus (SCN) functions as a seasonal clock through its ability to encode day length [1-6]. To investigate the mechanism by which SCN neurons code for day length, we housed mice under long (LD 16:8) and short (LD 8:16) photoperiods. Electrophysiological recordings of multiunit activity (MUA) in the SCN of freely moving mice revealed broad activity profiles in long days and compressed activity profiles in short days. The patterns remained consistent after release of the mice in constant darkness. Recordings of MUA in acutely prepared hypothalamic slices showed similar differences between the SCN electrical activity patterns in vitro in long and short days. In vitro recordings of neuronal subpopulations revealed that the width of the MUA activity profiles was determined by the distribution of phases of contributing units within the SCN. The subpopulation patterns displayed a significantly broader distribution in long days than in short days. Long-term recordings of single-unit activity revealed short durations of elevated activity in both short and long days (3.48 and 3.85 hr, respectively). The data indicate that coding for day length involves plasticity within SCN neuronal networks in which the phase distribution of oscillating neurons carries information on the photoperiod's duration. 相似文献
992.
Pégurier C Collart P Danhaive P Defays S Gillard M Gilson F Kogej T Pasau P Van Houtvin N Van Thuyne M van Keulen B 《Bioorganic & medicinal chemistry letters》2007,17(15):4228-4231
The discovery and optimization of a novel class of potent CCR3 antagonists is described. Details of synthesis and SAR are given together with some ADME properties of selected compounds. An optimal balance between activities, physicochemical properties, and in vitro metabolic stability was reached by the proper choice of substituents. 相似文献
993.
Laver M Schilperoord M 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2007,362(1485):1711-1721
Two important human action selection processes are the choice by citizens of parties to support in elections and the choice by party leaders of policy 'packages' offered to citizens in order to attract this support. Having reviewed approaches analysing these choices and the reasons for doing this using the methodology of agent-based modelling, we extend a recent agent-based model of party competition to treat the number and identity of political parties as an output of, rather than an input to, the process of party competition. Party birth is modelled as an endogenous change of agent type from citizen to party leader, which requires describing citizen dissatisfaction with the history of the system. Endogenous birth and death of parties transforms into a dynamic system even in an environment where all agents have otherwise non-responsive adaptive rules. A key parameter is the survival threshold, with lower thresholds leaving citizens on average less dissatisfied. Paradoxically, the adaptive rule most successful for party leaders in winning votes makes citizens on average less happy than under other policy-selection rules. 相似文献
994.
Amphiphilic polyether branched molecules to increase the circulation time of cationic particles 总被引:1,自引:0,他引:1
Garinot M Mignet N Largeau C Seguin J Scherman D Bessodes M 《Bioorganic & medicinal chemistry》2007,15(9):3176-3186
The preparation, physicochemical and biological properties of amphiphilic polyether branched molecules is described. These 'bunch shaped' molecules when inserted into cationic liposomes/DNA complexes have shown efficient surface charge shielding. As a consequence they efficiently inhibited the non specific interactions with blood components and significantly enhanced circulation time of the particles in the blood track. Formulations containing these molecules compared positively with those containing PEG lipids, providing a 5-fold increase in circulation time. 相似文献
995.
996.
Cationic lipids are efficient tools to introduce nucleic acids and proteins into cells. Elucidation of the mechanism and cellular pathways associated with such transport has been relatively tedious, even though significant progress has been made in the characterization of the intracellular trafficking of lipid/DNA complexes. Surprisingly little is known about the effects of these delivery vectors on cell functioning. In this report, we show that both cationic lipids and cationic lipid/DNA complexes mobilize the intracellular calcium. Removal of extracellular calcium did not significantly abolish this effect and preincubating cells with thapsigargin led to a decrease in [Ca2+]i, indicating that calcium was released mainly from internal calcium stores sensitive to thapsigargin. Pretreatment of the cells with the phospholipase C inhibitor U73122, blocked the [Ca2+]i rise, suggesting an inositol dependent mechanism. 相似文献
997.
Jacquot Y Broutin I Miclet E Nicaise M Lequin O Goasdoué N Joss C Karoyan P Desmadril M Ducruix A Lavielle S 《Bioorganic & medicinal chemistry》2007,15(3):1439-1447
Peptide ligands that disrupt MAPK pathways are of great interest for a better understanding of these signalling cascades and represent therefore an attractive target to control cell degenerative processes. In that context, selective disruption of the upstream Grb2/Sos complex in the Ras/MAPK cascade has focused extensive work. The Sos PPII decapeptide, which interacts with the Grb2-SH3 domains, has been modified in various positions and the best inhibitors designed so far are either dimeric ligands or peptoid analogues of the VPPPVPPRRR sequence. We report the synthesis of new Grb2 ligands in which the key Val5 residue has been replaced by a cis C(beta)-substituted proline. Both fluorescence and ITC assays have been employed to measure the affinity of these substituted peptides for a recombinant Grb2 protein. Whereas proline in position 5 completely abolished the binding potency, a cis C(beta)-methyl-L-proline restored the affinity. Other cis C(beta)-proline substituents led to a complete loss of binding potency. Combining the best modifications: a cis C(beta)-methylproline 5, N-acetylation, C-carboxamide and dimerization yielded a 560-fold affinity enhancement compared to the wild-type VPPPVPPRRR sequence. This study shows that C(beta)-substituted prolines may constitute a new alternative for PPII ligands, combining entropy and enthalpy beneficial effects. 相似文献
998.
Sacher F Jais P Stephenson K O'Neill MD Hocini M Clementy J Stevenson WG Haissaguerre M 《Indian pacing and electrophysiology journal》2007,7(1):1-6
Phrenic Nerve Injury (PNI) has been well studied by cardiac surgeons. More recently it has been recognized as a potential complication of catheter ablation with a prevalence of 0.11 to 0.48 % after atrial fibrillation (AF) ablation. This review will focus on PNI after AF ablation. Anatomical studies have shown a close relationship between the right phrenic nerve and it's proximity to the superior vena cava (SVC), and the antero-inferior part of the right superior pulmonary vein (RSPV). In addition, the proximity of the left phrenic nerve to the left atrial appendage has been well established. Independent of the type of ablation catheter (4 mm, 8 mm, irrigated tip, balloon) or energy source used (radiofrequency (RF), ultrasound, cryothermia, and laser); the risk of PNI exists during ablation at the critical areas listed above. Although up to thirty-one percent of patients with PNI after AF ablation remain asymptomatic, dyspnea remain the cardinal symptom and is present in all symptomatic patients. Despite the theoretical risk for significant adverse effect on functional status and quality of life, short-term outcomes from published studies appear favorable with 81% of patients with PNI having a complete recovery after 7 +/- 7 months. CONCLUSION: Existing studies have described PNI as an uncommon but avoidable complication in patients undergoing pulmonary vein isolation for AF. Prior to ablation at the SVC, antero-inferior RSPV ostium or the left atrial appendage, pacing should be performed before energy delivery. If phrenic nerve capture is documented, energy delivery should be avoided at this site. Electrophysiologist's vigilance as well as pacing prior to ablation at high risk sites in close proximity to the phrenic nerve are the currently available tools to avoid the complication of PNI. 相似文献
999.
1000.
Matthieu Guillemain Romain Blanc Christelle Lucas Michel Lepley 《Biodiversity and Conservation》2007,16(12):3633-3651
Ecotourism is becoming very popular, especially in protected areas where wildlife concentrate and is easier to observe, but
the consequences of associated disturbance have seldom be quantified other than in the short-term, making the sustainability
of this activity untested. We combined a historical, an empirical and an experimental approach to assess the long-, medium-
and short-term consequences of disturbance to wintering wildfowl (Anatidae) in a wetland of international importance in the Camargue, Southern France. In the short-term, disturbance made teal (Anas crecca) move away temporarily from observation blinds without leaving the waterbody. Wildfowl fed more after disturbance, disrupting
their normal resting activities. In the medium-term, waterbodies with more tourists did not host fewer birds: conversely the
most heavily disturbed one hosted the highest wildfowl density. In the long term, wildfowl numbers were not related with the
number of visitors. When practiced with appropriate guiding of people, and where appropriate facilities are provided to limit
human disturbance as done here, ecotourism may not affect wintering wildfowl other than reversibly in the very short term.
The legitimate demand of the public for access, even in fragile protected areas, may therefore be sustainable under some conditions. 相似文献