全文获取类型
收费全文 | 6515篇 |
免费 | 1034篇 |
国内免费 | 25篇 |
专业分类
耳鼻咽喉 | 49篇 |
儿科学 | 247篇 |
妇产科学 | 156篇 |
基础医学 | 944篇 |
口腔科学 | 150篇 |
临床医学 | 957篇 |
内科学 | 1146篇 |
皮肤病学 | 93篇 |
神经病学 | 801篇 |
特种医学 | 273篇 |
外国民族医学 | 1篇 |
外科学 | 684篇 |
综合类 | 516篇 |
一般理论 | 3篇 |
预防医学 | 507篇 |
眼科学 | 133篇 |
药学 | 609篇 |
中国医学 | 3篇 |
肿瘤学 | 302篇 |
出版年
2021年 | 75篇 |
2019年 | 77篇 |
2018年 | 105篇 |
2017年 | 74篇 |
2016年 | 78篇 |
2015年 | 103篇 |
2014年 | 150篇 |
2013年 | 231篇 |
2012年 | 263篇 |
2011年 | 288篇 |
2010年 | 160篇 |
2009年 | 143篇 |
2008年 | 226篇 |
2007年 | 268篇 |
2006年 | 259篇 |
2005年 | 282篇 |
2004年 | 254篇 |
2003年 | 249篇 |
2002年 | 250篇 |
2001年 | 214篇 |
2000年 | 222篇 |
1999年 | 208篇 |
1998年 | 126篇 |
1997年 | 95篇 |
1996年 | 100篇 |
1995年 | 89篇 |
1994年 | 83篇 |
1993年 | 87篇 |
1992年 | 153篇 |
1991年 | 168篇 |
1990年 | 139篇 |
1989年 | 178篇 |
1988年 | 137篇 |
1987年 | 194篇 |
1986年 | 146篇 |
1985年 | 136篇 |
1984年 | 123篇 |
1983年 | 110篇 |
1982年 | 89篇 |
1981年 | 96篇 |
1980年 | 108篇 |
1979年 | 103篇 |
1978年 | 67篇 |
1977年 | 71篇 |
1976年 | 58篇 |
1975年 | 59篇 |
1974年 | 69篇 |
1972年 | 70篇 |
1971年 | 49篇 |
1970年 | 51篇 |
排序方式: 共有7574条查询结果,搜索用时 15 毫秒
81.
Purification and characterization of an extracellular protease from Pseudomonas cepacia. 总被引:7,自引:6,他引:7 下载免费PDF全文
An extracellular proteinase (PSCP) produced by Pseudomonas cepacia was purified from culture supernatants by ammonium sulfate precipitation, anion exchange chromatography on DEAE-Sephacel, and G200 gel filtration chromatography. The protease has an apparent Mr of 34,000 by electrophoresis. Substrates cleaved by the protease include gelatin, hide powder, and collagen but not human immunoglobulin G (IgG), IgM, secretory IgA, or IgA. The enzyme had the characteristics of a metalloprotease, a pH optimum of 6, and a temperature optimum of 45 degrees C. Intratracheal instillation of purified PSCP into rat lungs produced a bronchopneumonia characterized by polymorphonuclear cell infiltration and proteinaceous exudation into large airways. Rats responded immunologically to active immunization with PSCP, but this response was not protective against subsequent lung infection with P. cepacia. PSCP was shown to have antigenic similarity with Pseudomonas aeruginosa elastase by an immunoblotting technique. Sera from 10 cystic fibrosis patients, with and without a previous history of P. cepacia colonization, were shown to possess antibody reactive against PSCP. 相似文献
82.
83.
Carol M. Woods Jack L. Vevea Dianne L. Chambless Ute J. Bayen 《Clinical psychology》2002,9(4):353-366
Researchers have hypothesized that compulsive checkers suffer from impairment in explicit memory (e.g., Sher, Frost, & Otto, 1983 ), low confidence in explicit memory (e.g., McNally & Kohlbeck, 1993 ), or both. However, empirical findings have been equivocal, possibly due to variability in effect sizes produced by small samples. Combining data across studies may yield more meaningful conclusions than can be surmised from a narrative review. Following a brief review of the literature on checking and memory, we present meta-analytic results suggesting that checkers are impaired on many types of memory tasks (e.g., verbal free recall, verbal cued recall, and recall of actions) and are less confident in recognition than noncheckers. We discuss implications of these findings, suggestions for future research, and limitations of this analysis. 相似文献
84.
An ellipsoidal particle, measuring 450 x 150 nm, from honey bees comprises a nucleocapsid measuring 3000 x 40 nm, containing double-stranded DNA with a molecular weight of approximately 12 x 10(6), which is coiled within a membrane. The buoyant densities in CsCl of the whole particle, nucleocapsid, DNA and DNA with ethidium bromide are 1.28, 1.36, 1.71 and 1.61 g/ml, respectively. The particle contains about 12 proteins, with molecular weights ranging from 13,000 to 70,000, which are distributed approximately equally between the membrane and the nucleocapsid. 相似文献
85.
Protective cytotoxic T lymphocyte responses against paramyxoviruses induced by epitope-based DNA vaccines: involvement of IFN-gamma 总被引:1,自引:0,他引:1
Hsu SC; Obeid OE; Collins M; Iqbal M; Chargelegue D; Steward MW 《International immunology》1998,10(10):1441-1447
Plasmid DNA vectors have been constructed with minigenes encoding a single
cytotoxic T lymphocyte (CTL) epitope from either the M2 protein of
respiratory syncytial virus (RSV) or from the nucleoprotein of measles
virus (MV) with or without a signal sequence (also called secretory or
leader sequence). Following intradermal immunization, plasmids in which the
CTL epitopes were expressed in-frame with the signal sequence were more
effective at inducing peptide- and virus- specific CTL responses than
plasmids expressing CTL epitopes without the signal sequence. This
immunization resulted in protection against MV-induced encephalitis and a
significant reduction in viral load following RSV challenge. The reduction
of viral load following RSV challenge was abrogated by prior injection with
anti-IFN-gamma antibodies. These results highlight the ability of
epitope-based DNA immunization to induce protective immune responses to
well-defined epitopes and indicate the potential of this approach for the
development of vaccines against infectious diseases.
相似文献
86.
Fear-Potentiated Startle in Humans: Effects of Anticipatory Anxiety on the Acoustic Blink Reflex 总被引:7,自引:0,他引:7
Christian Grillon Rezvan AMELI Scott W. Woods Kathleen Merikangas Michael Davis 《Psychophysiology》1991,28(5):588-595
The effects of fear/anticipatory anxiety on the acoustic startle reflex were investigated in humans using a paradigm involving anticipation of electric shocks. The eyeblink component of the startle reflex, elicited by an abrupt auditory stimulus, was measured in 9 normal volunteers during either the anticipation of electric shocks (anticipatory anxiety) or periods in which no shocks were anticipated (safe period). The eyeblink was consistently higher in amplitude, and shorter in latency, during periods when the subjects anticipated shocks, compared to the safe periods. This effect could not be attributed solely to a reduction in habituation and was statistically significant before the subjects actually received any shock (a single 30 mA stimulation on the median nerve). These results indicate that anticipatory anxiety can be measured objectively in humans using the fear-potentiated startle reflex in a paradigm not actually requiring any shock. Because a great deal is known about the neuroanatomical and pharmacological mechanisms of fear-potentiated startle in laboratory animals, this test procedure may be especially useful in humans to investigate the neurobiological substrates of anxiety disorders and their pharmacological treatments. 相似文献
87.
Evaluation of MicroScan MIC panels for detection of oxacillin-resistant staphylococci. 总被引:2,自引:1,他引:2 下载免费PDF全文
Clinical isolates of staphylococci (420 Staphylococcus aureus isolates and 248 coagulase-negative staphylococci) were tested by both MicroScan MIC panels (MicroScan, West Sacramento, Calif.) and an oxacillin agar screen (Mueller-Hinton agar [Difco Laboratories, Detroit, Mich.] containing 6 micrograms of oxacillin per ml and 4% NaCl) to evaluate the ability of MicroScan to detect oxacillin-resistant strains. MicroScan panels and oxacillin agar screen plates were incubated at 35 degrees C for 24 h and at 30 degrees C for an additional 24 h. Endpoints were recorded at 24 and 48 h. By MicroScan, 23 (5.5%) and 30 (7%) S. aureus isolates and 161 (65%) and 162 (65%) coagulase-negative staphylococci were oxacillin resistant at 24 and 48 h, respectively. At both 24 and 48 h, 23 (5.5%) S. aureus isolates and 162 (65%) coagulase-negative staphylococci were resistant by the oxacillin agar screen. Five strains for which the oxacillin MIC was 2 or 4 micrograms/ml and eight strains resistant to oxacillin only at 48 h were further evaluated by broth macrodilution testing for oxacillin with and without clavulanic acid, by oxacillin and amoxicillin-clavulanic acid disk diffusion, and by oxacillin agar screen comparing Mueller-Hinton agars purchased from Difco and BBL Microbiology Systems, Cockeysville, Md. By this additional testing, all 10 S. aureus isolates and 1 of 3 coagulase-negative staphylococci examined produced increased amounts of beta-lactamase. One coagulase-negative staphylococcus appeared to be truly intermediately oxacillin susceptible. There was no significant difference in the rate of detection of oxacillin resistance between MicroScan and the agar screen. MicroScan panels should be incubated for 24 h only, because prolonged incubation caused strains producing excessive amounts of beta-lactamase to appear to be falsely oxacillin resistant. 相似文献
88.
A-549 cells were compared with other cell lines for virus recovery, except from specimens submitted specifically for detection of cytomegalovirus. Of 589 specimens submitted specifically for detection of herpes simplex virus (HSV), 163 (28%) were positive for HSV--159 (97.5%) in A-549 cells and 156 (96%) in primary rabbit kidney cells. HSV cytopathic effect was identified an average of 0.6 day earlier in A-549 cells. Virus was recovered from 194 (11%) of 1,790 specimens submitted for general virus isolation. Of 40 HSV isolates, 85% were positive in A-549 cells, 72.5% were positive in MRC-5/WI-38 cells, and 42.5% were positive in HEp-2 cells. With adenovirus, 96% of 45 isolates were detected in A-549 cells, 62% were detected in HEp-2 cells, 38% were detected in MRC-5/WI-38 cells, and 31% were detected in PMK cells. Of the 76 enterovirus-positive specimens, 71% were positive in PMK cells, 62% were positive in A-549 cells, and 62% were positive in MRC-5/WI-38 cells. None of 12 respiratory syncytial virus, 14 rhinovirus, or 7 influenza A virus isolates were detected in A-549 cells. Of the cell lines examined, A-549 cells performed optimally for recovery of HSV and adenovirus, they allowed good growth of many of the enterovirus isolates, but they did not allow recovery of any of the respiratory syncytial virus, rhinovirus, or influenza A virus isolates. 相似文献
89.
Molecular epidemiology of Legionella species by restriction endonuclease and alloenzyme analysis. 总被引:7,自引:20,他引:7 下载免费PDF全文
L S Tompkins N J Troup T Woods W Bibb R M McKinney 《Journal of clinical microbiology》1987,25(10):1875-1880
As part of an ongoing investigation into nosocomial Legionella infections at Stanford University Medical Center (SUMC), we applied the technique of restriction endonuclease analysis (REA) to determine strain differences among three species, including Legionella pneumophila, Legionella dumoffii, and Legionella micdadei. A total of 26 human and environmental water isolates from SUMC were selected for REA and compared with control strains that were not epidemiologically linked to SUMC. REA results were compared with results of alloenzyme typing, typing by monoclonal antibodies, and plasmid fingerprinting in all but L. micdadei strains. REA and alloenzyme typing showed that SUMC patient isolates were derived from distinct strains of three species. L. pneumophila strains from SUMC patients were genotypically identical to those isolated from potable water. REA was especially useful in proving that SUMC L. dumoffii patient isolates were derived from a single strain and that patients may have been exposed to a common source(s). REA typing correlated well with alloenzyme typing. These methods complement serologic typing of L. pneumophila and provide discriminating capability between strains of other Legionella species such as L. dumoffii, for which serologic types have not been identified. In addition, REA typing is somewhat easier to perform than alloenzyme typing and can be done in clinical laboratories. 相似文献
90.
Teemu Rinne Siiri Kirjavainen Oili Salonen Alexander Degerman Xiaojian Kang David L. Woods Kimmo Alho 《Neuroscience letters》2007
We used behavioral measures and functional magnetic resonance imaging (fMRI) to study the effects of parametrically varied task-irrelevant pitch changes in attended sounds on loudness-discrimination performance and brain activity in cortical surface maps. Ten subjects discriminated tone loudness in sequences that also included infrequent task-irrelevant pitch changes. Consistent with results of previous studies, the task-irrelevant pitch changes impaired performance in the loudness discrimination task. Auditory stimulation, attention-enhanced processing of sounds and motor responding during the loudness discrimination task activated supratemporal (auditory cortex) and inferior parietal areas bilaterally and left-hemisphere (contralateral to the hand used for responding) motor areas. Large pitch changes were associated with right hemisphere supratemporal activations as well as widespread bilateral activations in the frontal lobe and along the intraparietal sulcus. Loudness discrimination and distracting pitch changes activated common areas in the right supratemporal gyrus, left medial frontal cortex, left precentral gyrus, and left inferior parietal cortex. 相似文献