全文获取类型
收费全文 | 13262篇 |
免费 | 1423篇 |
国内免费 | 2417篇 |
出版年
2023年 | 134篇 |
2022年 | 208篇 |
2021年 | 179篇 |
2020年 | 197篇 |
2019年 | 205篇 |
2018年 | 242篇 |
2017年 | 174篇 |
2016年 | 224篇 |
2015年 | 257篇 |
2014年 | 389篇 |
2013年 | 226篇 |
2012年 | 1062篇 |
2011年 | 1147篇 |
2010年 | 344篇 |
2009年 | 303篇 |
2008年 | 1001篇 |
2007年 | 954篇 |
2006年 | 976篇 |
2005年 | 964篇 |
2004年 | 957篇 |
2003年 | 891篇 |
2002年 | 720篇 |
2001年 | 701篇 |
2000年 | 822篇 |
1999年 | 429篇 |
1998年 | 235篇 |
1997年 | 248篇 |
1996年 | 218篇 |
1995年 | 187篇 |
1994年 | 204篇 |
1993年 | 203篇 |
1992年 | 242篇 |
1991年 | 191篇 |
1990年 | 164篇 |
1989年 | 147篇 |
1988年 | 104篇 |
1987年 | 76篇 |
1986年 | 102篇 |
1985年 | 88篇 |
1984年 | 88篇 |
1983年 | 72篇 |
1982年 | 78篇 |
1981年 | 66篇 |
1980年 | 52篇 |
1979年 | 35篇 |
1959年 | 31篇 |
1958年 | 37篇 |
1957年 | 54篇 |
1954年 | 32篇 |
1953年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
Jabor MA Shayani P Collins DR Karas T Cohen BE 《Plastic and reconstructive surgery》2002,110(2):457-63; discussion 464-5
After performing a chart review, the authors identified 120 patients who underwent breast cancer-related reconstruction. All charts were evaluated with regard to breast mound reconstruction type, nipple-areola reconstruction type, the interval between breast mound and nipple-areola reconstruction, the number of procedures needed to achieve nipple-areola reconstruction, patient history of radiation therapy, and complications. A questionnaire was then developed and mailed to all of the patients who underwent both breast mound and nipple/areola reconstruction (n = 105) to evaluate their level of satisfaction. Of the 43 patients who returned the questionnaire, 41 completed all portions correctly. The questionnaire evaluated patient satisfaction with breast mound reconstruction; patient satisfaction with nipple-areola reconstruction; what the patient disliked most about the nipple-areola reconstruction; and whether or not the patient would choose to have breast reconstruction again. Several parameters were then tested statistically against the reported patient satisfaction.A review of all patients who underwent breast reconstruction revealed that their breast mound reconstructions were done using either a TRAM flap (59 percent), a latissimus dorsi flap and an implant (19 percent), an expander followed by an implant (9 percent), an implant only (4 percent), or other means (9 percent). The nipple-areola was reconstructed in these patients with either a star flap (36 percent), nipple sharing (10 percent), a keyhole flap (9 percent), a skate flap (9 percent), an S-flap (8 percent), a full-thickness skin graft (6 percent), or by another means (22 percent). The number of procedures needed to achieve nipple-areola reconstruction was either one (in 66 percent of the patients), two (in 32 percent of the patients), or three or more (2 percent of the patients). Eleven percent of the patients experienced the complication of nipple necrosis.Satisfaction with breast mound reconstruction was reported by 81 percent of patients to be excellent/good, by 14 percent of patients to be fair, and by 5 percent of patients to be poor. Reported satisfaction with nipple-areola reconstruction was excellent/good for 64 percent of patients, fair for 22 percent of patients, and poor for 14 percent of patients. The factors patients disliked most about their nipple-areola reconstruction were, in descending order, lack of projection, color match, shape, size, texture, and position. Statistical analysis of the data revealed inferior patient satisfaction when there was a longer interval between breast mound and nipple areola reconstruction (p = 0.003). No significant difference was observed in nipple/areola reconstruction satisfaction ratings when compared with breast mound reconstruction type (p = 0.46), nipple-areola reconstruction type (p = 0.98), and history of radiation therapy (p = 0.23). There was also no significant difference when breast mound reconstruction was compared with technique (p = 0.51) and history of radiation therapy (p = 0.079). Overall, there was a greater satisfaction with breast mound reconstruction than with nipple-areola reconstruction (p = 0.0001). 相似文献
992.
Lohrke SM Dery PD Li W Reedy R Kobayashi DY Roberts DR 《Molecular plant-microbe interactions : MPMI》2002,15(8):817-825
Strains of Enterobacter cloacae show promise as biocontrol agents for Pythium ultimum-induced damping-off on cucumber and other crops. E. cloacae A145 is a mini-Tn5 Km transposon mutant of strain 501R3 that was significantly reduced in suppression of damping-off on cucumber caused by P. ultimum. Strain A145 was deficient in colonization of cucumber, sunflower, and wheat seeds and significantly reduced in colonization of corn and cowpea seeds relative to strain 501R3. Populations of strain A145 were also significantly lower than those of strain 501R3 at all sampling times in cucumber, wheat, and sunflower rhizosphere. Populations of strain A145 were not detectable in any rhizosphere after 42 days, while populations of strain 501R3 remained at substantial levels throughout all experiments. Molecular characterization of strain A145 indicated mini-Tn5 Km was inserted in a region of the E. cloacae genome with a high degree of DNA and amino acid sequence similarity to rpiA, which encodes ribose-5-phosphate isomerase. In Escherichia coli, RpiA catalyzes the interconversion of ribose-5-phosphate and ribulose-5-phosphate and is a key enzyme in the pentose phosphate pathway. Ribose-5-phosphate isomerase activity in cell lysates from strain A145 was approximately 3.5% of that from strain 501R3. In addition, strain A145 was a ribose auxotroph, as expected for an rpiA mutant. Introduction of a 1.0-kb DNA fragment containing only the rpiA homologue into strain A145 restored ribose phosphate isomerase activity, prototrophy, seedling colonization, and disease suppression to levels similar to those associated with strain 501R3. Experiments reported here indicate a key role for rpiA and possibly the pentose phosphate pathway in suppression of damping-off and colonization of subterranean portions of plants by E. cloacae. 相似文献
993.
Price BM Barten Legutki J Galloway DR von Specht BU Gilleland LB Gilleland HE Staczek J 《FEMS immunology and medical microbiology》2002,33(2):89-99
The outer membrane protein F gene (oprF) of Pseudomonas aeruginosa was recently shown by us to protect mice from P. aeruginosa chronic pulmonary infection when used as a DNA vaccine administered by three biolistic (gene gun) intradermal inoculations given at 2-week intervals. In the present study, we used two different strategies to improve the protective efficacy of the DNA vaccine. In the first strategy, mice were primed with two biolistic intradermal inoculations with the oprF vaccine and then were given a final intramuscular booster immunization containing either a synthetic peptide-keyhole limpet hemocyanin (KLH) conjugate or a chimeric influenza virus. Both the synthetic peptide conjugate and the chimeric virus contained peptide 10, a previously identified immunoprotective epitope of protein F. The second strategy involved the addition of a second outer membrane protein to the vaccine. DNA encoding a fusion protein comprised of the C-terminal half of protein F fused to OprI was administered by three biolistic intradermal inoculations. Challenge with P. aeruginosa in a chronic pulmonary infection model demonstrated that boosting with the chimeric virus (but not with peptide-KLH) or adding oprI to the DNA vaccine significantly enhanced protection as compared to that afforded by the oprF vaccine given alone. Thus, both strategies appear to augment the protection afforded by an oprF-only DNA vaccine. 相似文献
994.
Broad-host-range plasmid RK2 encodes a post-segregational killing system, parDE, which contributes to the stable maintenance of this plasmid in Escherichia coli and many distantly related bacteria. The ParE protein is a toxin that inhibits cell growth, causes cell filamentation and eventually cell death. The ParD protein is a specific ParE antitoxin. In this work, the in vitro activities of these two proteins were examined. The ParE protein was found to inhibit DNA synthesis using an E. coli oriC supercoiled template and a replication-proficient E. coli extract. Moreover, ParE inhibited the early stages of both chromosomal and plasmid DNA replication, as measured by the DnaB helicase- and gyrase-dependent formation of FI*, a highly unwound form of supercoiled DNA. The presence of ParD prevented these inhibitory activities of ParE. We also observed that the addition of ParE to supercoiled DNA plus gyrase alone resulted in the formation of a cleavable gyrase-DNA complex that was converted to a linear DNA form upon addition of sodium dodecyl sulphate (SDS). Adding ParD before or after the addition of ParE prevented the formation of this cleavable complex. These results demonstrate that the target of ParE toxin activity in vitro is E. coli gyrase. 相似文献
995.
996.
Tschantz DR Crockett EL Niewiarowski PH Londraville RL 《Physiological and biochemical zoology : PBZ》2002,75(6):544-556
We tested the hypothesis that the physiological strategy for acclimating to low body temperature is similar among closely related fish. Largemouth bass (Micropterus salmoides), green sunfish (Lepomis cyanellus), bluegill sunfish (Lepomis macrochirus), black crappie (Pomonix nigromaculatus), and white crappie (Pomonix annularis), all members of the family Centrarchidae, were acclimated to 5 degrees and 25 degrees C. Morphometric variables (total mass, total length, organ masses) and enzyme activities (hexokinase; lactate dehydrogenase; and cytochrome oxidase in heart, liver, and muscle) were measured in 5 degrees C- and 25 degrees C-acclimated fish at 5 degrees and 25 degrees C assay temperatures. Each species displayed a distinct physiological response to cold acclimation that differed among tissues. These data suggest that the response to cold acclimation is highly variable within families. Our findings are consistent with other studies suggesting that acclimation responses are labile and may evolve independently even among closely related species. 相似文献
997.
998.
999.
Leptin acts within the hypothalamus to diminish food intake. During pregnancy and lactation, both circulating leptin concentrations and food intake are elevated, suggesting an ineffectiveness of leptin to reduce food intake in these mice. Thus, this study tested the ability of intracerebroventricular (ICV) leptin administration to alter food intake during pregnancy and lactation. Mice during the first, second, and third trimesters of pregnancy, lactating mice on postpartum Day 7, and age-matched female mice were used. Plasma leptin concentrations averaged 2.9 +/- 0.3 ng/ml in control mice, increased steadily as pregnancy progressed (3.4 +/- 0.7, 29.8 +/- 4.5, and 40.5 +/- 0.7 ng/ml during the first, second, and third trimesters, respectively), and remained elevated on Day 7 postpartum (26.4 +/- 7.8 ng/ml). Mice were food deprived for 4 h, injected ICV with vehicle or leptin (1 micro g), and food intake was subsequently measured hourly for 3 hr, and after 24 hr. Vehicle-treated pregnant mice consumed marginally more food than cycling control mice, whereas nursing dams ate two to three times as much food as controls. As expected, ICV leptin administration reduced 24-hr food intake of control mice by 2 g, or approximately 50%. ICV-administered leptin was as effective in reducing food intake of pregnant and lactating mice as observed in control mice. Thus, the elevated circulating leptin concentrations observed in pregnant and nursing mice did not alter the ability of ICV-administered leptin to diminish food intake. High plasma concentrations of leptin-binding proteins observed during pregnancy, and probably during lactation, may limit the amount of endogenous leptin reaching the hypothalamus, and may consequently enable increases in food intake concomitant with elevated plasma leptin during these nutritionally demanding periods. 相似文献
1000.