全文获取类型
收费全文 | 15837篇 |
免费 | 1416篇 |
国内免费 | 12篇 |
出版年
2023年 | 76篇 |
2022年 | 135篇 |
2021年 | 280篇 |
2020年 | 123篇 |
2019年 | 178篇 |
2018年 | 246篇 |
2017年 | 200篇 |
2016年 | 345篇 |
2015年 | 593篇 |
2014年 | 711篇 |
2013年 | 941篇 |
2012年 | 1053篇 |
2011年 | 1105篇 |
2010年 | 687篇 |
2009年 | 608篇 |
2008年 | 919篇 |
2007年 | 974篇 |
2006年 | 870篇 |
2005年 | 812篇 |
2004年 | 803篇 |
2003年 | 779篇 |
2002年 | 697篇 |
2001年 | 275篇 |
2000年 | 220篇 |
1999年 | 254篇 |
1998年 | 242篇 |
1997年 | 162篇 |
1996年 | 146篇 |
1995年 | 157篇 |
1994年 | 154篇 |
1993年 | 151篇 |
1992年 | 180篇 |
1991年 | 125篇 |
1990年 | 171篇 |
1989年 | 126篇 |
1988年 | 121篇 |
1987年 | 113篇 |
1986年 | 97篇 |
1985年 | 92篇 |
1984年 | 86篇 |
1983年 | 85篇 |
1982年 | 80篇 |
1981年 | 83篇 |
1980年 | 90篇 |
1979年 | 88篇 |
1977年 | 64篇 |
1976年 | 65篇 |
1974年 | 55篇 |
1973年 | 49篇 |
1971年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
We explored changes in ocean pH in coastal Washington state, USA, by extending a decadal-scale pH data series, by reporting independent measures of dissolved inorganic carbon (DIC), spectrophotometric pH, and total alkalinity (TA), by exploring pH patterns over larger spatial scales, and by probing for long-term trends in environmental variables reflecting potentially important drivers of pH. We found that pH continued to decline in this area at a rapid rate, that pH exhibited high natural variability within years, that our measurements of pH corresponded well to spectrophotometric pH measures and expected pH calculated from DIC/TA, and that TA estimates based on salinity predicted well actual alkalinity. Multiple datasets reflecting upwelling, including water temperature, nutrient levels, phytoplankton abundance, the NOAA upwelling index, and data on local wind patterns showed no consistent trends over the period of our study. Multiple datasets reflecting precipitation change and freshwater runoff, including precipitation records, local and regional river discharge, salinity, nitrate and sulfate in rainwater, and dissolved organic carbon (DOC) in rivers also showed no consistent trends over time. Dissolved oxygen did not decline over time, indicating that long-term changes did not result from shifts in contributions of respiration to pH levels. These tests of multiple potential drivers of the observed rapid rate of pH decline indicate a primary role for inorganic carbon and suggest that geochemical models of coastal ocean carbon fluxes need increased investigation. 相似文献
22.
S. Clarke 《BMJ (Clinical research ed.)》1992,304(6832):961-963
OBJECTIVE--To identify the attitudes of general practitioners towards the use of thermometers in general practice. DESIGN--Postal questionnaire survey. SETTING--All general practitioners in the catchment area of Frimley Park Hospital, Surrey. SUBJECTS--145 general practitioners. MAIN OUTCOME MEASURES--Answers to questions covering a variety of aspects concerning the use of thermometers in general practice. RESULTS--116 (80%) doctors replied. Seven doctors did not have any method of taking a patient''s temperature; up to 12 more doctors did not use their thermometers and 56 doctors used them infrequently, less than once a fortnight. Mercury glass thermometers were most commonly used (80 doctors; 69%), but only 8% of doctors used them correctly. Six doctors failed to clean their thermometers between patients. The study failed to identify the roles of axillary and rectal temperature readings. CONCLUSION--There is a wide variation in attitudes towards the use of thermometers in general practice. 相似文献
23.
24.
Mary Margaret Huizinga Sara N. Bleich Mary Catherine Beach Jeanne M. Clark Lisa A. Cooper 《Obesity (Silver Spring, Md.)》2010,18(10):1932-1937
Physician perception of medication adherence may alter prescribing patterns. Perception of patients has been linked to readily observable factors, such as race and age. Obesity shares a similar stigma to these factors in society. We hypothesized that physicians would perceive patients with a higher BMI as nonadherent to medication. Data were collected from the baseline visit of a randomized clinical trial of patient–physician communication (240 patients and 40 physicians). Physician perception of patient medication adherence was measured on a Likert scale and dichotomized as fully adherent or not fully adherent. BMI was the predictor of interest. We performed Poisson regression analyses with robust variance estimates, adjusting for clustering of patients within physicians, to examine the association between BMI and physician perception of medication adherence. The mean (s.d.) BMI was 32.6 (7.7) kg/m2. Forty‐five percent of patients were perceived as nonadherent to medications by their physicians. Higher BMI was significantly and negatively associated with being perceived as adherent to medication (prevalence ratio (PrR) 0.76, 95% confidence interval (CI): 0.64–0.90; P = 0.002; per 10 kg/m2 increase in BMI). BMI remained significantly and negatively associated with physician perception of medication adherence after adjustment for patient and physician characteristics (PrR 0.80, 95% CI: 0.66–0.96; P = 0.020). In this study, patients with higher BMI were less likely to be perceived as adherent to medications by their providers. Physician perception of medication adherence has been shown to affect prescribing patterns in other studies. More work is needed to understand how this perception may affect the care of patients with obesity. 相似文献
25.
26.
Catherine Bonaïti-Pellié Françoise Clerget-Darpoux Marie-Claude Babron 《Human genetics》1990,86(2):203-208
Summary Although the retinoblastoma gene has been isolated and sequenced, the difference in penetrance and expressivity among families has not yet been fully explained. Balanced chromosomal insertion involving the 13q14 regions has been shown to account for some families with several unaffected carriers. Since there could be cases with karyotypically undetectable insertions, we tested whether this mechanism was general enough to explain the whole difference in expressivity among families. Using 166 pedigrees, reported in nine series available in the literature (including our own), we conclude that balanced insertion cannot entirely explain the familial data, even if we allow for a reduced viability of unbalanced gametes. Other mechanisms are proposed and discussed in this paper. 相似文献
27.
28.
Scaling of metabolic rate with body mass and temperature in teleost fish 总被引:27,自引:0,他引:27
29.
Nicolas Lamassiaude Berthine Toubate Cdric Neveu Pierre Charnet Catherine Dupuy Franoise Debierre-Grockiego Isabelle Dimier-Poisson Claude L. Charvet 《PLoS pathogens》2021,17(2)
Control of infestation by cosmopolitan lice (Pediculus humanus) is increasingly difficult due to the transmission of parasites resistant to pediculicides. However, since the targets for pediculicides have no been identified in human lice so far, their mechanisms of action remain largely unknown. The macrocyclic lactone ivermectin is active against a broad range of insects including human lice. Isoxazolines are a new chemical class exhibiting a strong insecticidal potential. They preferentially act on the γ-aminobutyric acid (GABA) receptor made of the resistant to dieldrin (RDL) subunit and, to a lesser extent on glutamate-gated chloride channels (GluCls) in some species. Here, we addressed the pediculicidal potential of isoxazolines and deciphered the molecular targets of ivermectin and the ectoparasiticide lotilaner in the human body louse species Pediculus humanus humanus. Using toxicity bioassays, we showed that fipronil, ivermectin and lotilaner are efficient pediculicides on adult lice. The RDL (Phh-RDL) and GluCl (Phh-GluCl) subunits were cloned and characterized by two-electrode voltage clamp electrophysiology in Xenopus laevis oocytes. Phh-RDL and Phh-GluCl formed functional homomeric receptors respectively gated by GABA and L-glutamate with EC50 values of 16.0 μM and 9.3 μM. Importantly, ivermectin displayed a super agonist action on Phh-GluCl, whereas Phh-RDL receptors were weakly affected. Reversally, lotilaner strongly inhibited the GABA-evoked currents in Phh-RDL with an IC50 value of 40.7 nM, whereas it had no effect on Phh-GluCl. We report here for the first time the insecticidal activity of isoxazolines on human ectoparasites and reveal the mode of action of ivermectin and lotilaner on GluCl and RDL channels from human lice. These results emphasize an expected extension of the use of the isoxazoline drug class as new pediculicidal agents to tackle resistant-louse infestations in humans. 相似文献
30.