全文获取类型
收费全文 | 3644篇 |
免费 | 242篇 |
国内免费 | 48篇 |
专业分类
耳鼻咽喉 | 32篇 |
儿科学 | 121篇 |
妇产科学 | 113篇 |
基础医学 | 323篇 |
口腔科学 | 139篇 |
临床医学 | 534篇 |
内科学 | 586篇 |
皮肤病学 | 55篇 |
神经病学 | 149篇 |
特种医学 | 380篇 |
外科学 | 450篇 |
综合类 | 243篇 |
一般理论 | 3篇 |
预防医学 | 329篇 |
眼科学 | 41篇 |
药学 | 202篇 |
2篇 | |
中国医学 | 34篇 |
肿瘤学 | 198篇 |
出版年
2022年 | 48篇 |
2021年 | 51篇 |
2020年 | 43篇 |
2019年 | 26篇 |
2018年 | 46篇 |
2017年 | 47篇 |
2016年 | 40篇 |
2015年 | 71篇 |
2014年 | 99篇 |
2013年 | 129篇 |
2012年 | 145篇 |
2011年 | 171篇 |
2010年 | 126篇 |
2009年 | 136篇 |
2008年 | 120篇 |
2007年 | 135篇 |
2006年 | 163篇 |
2005年 | 121篇 |
2004年 | 105篇 |
2003年 | 118篇 |
2002年 | 113篇 |
2001年 | 77篇 |
2000年 | 96篇 |
1999年 | 68篇 |
1998年 | 100篇 |
1997年 | 90篇 |
1996年 | 84篇 |
1995年 | 80篇 |
1994年 | 56篇 |
1993年 | 65篇 |
1992年 | 58篇 |
1991年 | 64篇 |
1990年 | 59篇 |
1989年 | 67篇 |
1988年 | 84篇 |
1987年 | 85篇 |
1986年 | 66篇 |
1985年 | 70篇 |
1984年 | 56篇 |
1983年 | 38篇 |
1982年 | 30篇 |
1981年 | 25篇 |
1980年 | 23篇 |
1977年 | 25篇 |
1976年 | 23篇 |
1959年 | 22篇 |
1958年 | 30篇 |
1956年 | 30篇 |
1955年 | 42篇 |
1954年 | 35篇 |
排序方式: 共有3934条查询结果,搜索用时 140 毫秒
51.
Extraskeletal myxoid chondrosarcoma: a clinicopathologic, immunohistochemical, and ploidy analysis of 23 cases. 总被引:3,自引:0,他引:3
A M Oliveira T J Sebo J E McGrory T A Gaffey M G Rock A G Nascimento 《Modern pathology》2000,13(8):900-908
Twenty-three cases of extraskeletal myxoid chondrosarcoma, evaluated at the Mayo Clinic between 1968 and 1996, were studied for clinicopathologic features, immunohistochemical profile, Ki-67 activity, and ploidy status to identify adverse prognostic factors. Females and males were equally affected, and the median age at diagnosis was 50 years. The tumors were located mainly in the lower extremities (83%), and the median tumor size was 9.5 cm. Sixteen tumors showed low cellularity (70%), and eight tumors had high mitotic activity (more than two per 10 high-power fields). The tumors were immunoreactive for vimentin (89%), synaptophysin (72%), epithelial membrane antigen (28%), and S-100 protein (17%). Nine tumors were diploid, three aneuploid, and one tetraploid. Mean Ki-67 activity was 11% (range, 1 to 45%). The 10-year overall survival rate was 78%. On univariate analysis, tumor size > or = 10 cm, high cellularity, presence of anaplasia or rhabdoid features, mitotic activity more than two per 10 high-power fields, Ki-67 > or = 10%, and Ki-67 "hot spot" > or = 25% were associated with decreased metastasis-free or overall survival. Ploidy status was not associated with any adverse outcome. The presence of any of these adverse prognostic factors can indicate the possibility of a more aggressive behavior in extraskeletal myxoid chondrosarcoma, and a closer follow-up is suggested. 相似文献
52.
Reciprocal effect of Waardenburg syndrome mutations on DNA binding by the Pax-3 paired domain and homeodomain 总被引:1,自引:1,他引:1
The Pax-3 protein contains two DNA-binding domains, a paired domain and a
homeodomain. Mutations in Pax-3 cause Waardenburg syndrome (WS) in humans
and the mouse Splotch (Sp) phenotype. In the Sp-delayed mouse, a mutation
in the Pax-3 paired domain (G9R) abrogates the DNA-binding activity of both
the paired domain and the homeodomain, suggesting that they may
functionally interact. To investigate this possibility further, we have
analyzed the DNA-binding properties of additional point mutants in the
Pax-3 paired domain and homeodomain that occur in WS patients (F12L, N14H,
G15S, P17L, R23L, G48A, S51F and G66D in the paired domain, V47F and R53G
in the homeodomain), the Pax-1 un mutation (G15A) and a substitution
associated with Peters' anomaly in the PAX-6 gene (R23G). Within the paired
domain, seven of 10 mutations were found to abrogate DNA-binding by the
paired domain. Remarkably, these seven mutations also affected DNA binding
by the homeodomain, causing either a complete loss (P17L and G66D), a
reduction (R23G, R23L, G15S and G15A) or an increase in DNA-binding
activity (N14H). In addition, the effect of paired domain mutations
occurred at the level of monomer formation by the homeodomain, while the
dimerization potential of this domain seemed unaffected in mutants where it
could be analyzed. Furthermore, while both homeodomain mutations were found
to abolish DNA binding by this domain, the R53G mutation also abrogated DNA
binding by the paired domain. The important observation that independent
mutations in either domain can affect DNA binding by the other in the
intact Pax- 3 protein strongly suggests that the two domains are not
functionally independent but bind DNA through cooperative interactions.
Modeling the deleterlous mutations on the three-dimensional structure of
the paired domain of Drosophila Prd shows that these mutations cluster at
the DNA interface, thus suggesting that a series of DNA contacts are
essential for DNA binding by both the paired domain and the homeodomain of
Pax-3.
相似文献
53.
Kucharczyk W; Brant-Zawadzki M; Lemme-Plaghos L; Uske A; Kjos B; Feinberg DA; Norman D 《Radiology》1985,157(1):95-101
In multiple spin-echo image sequences of blood flow, the "even-echo" phenomenon produces an absolute increase in signal magnitude from first- to second-echo images of normal vessels harboring slow flow. Distinguishing this from the apparent relatively high signal intensity seen on second-echo images in pathologic foci of stationary tissue is important to the diagnostician. Selected case material containing two tissue types was reviewed retrospectively: tissues known to harbor slow flow, such as normal veins and venous sinuses and vascular malformations, and tissues that have long transverse (T2) relaxation times and appear as intense structures on second-echo images, such as neoplasms, infarcts, and regions of demyelination. Calculations of T2 parameters were made by computer for defined regions of interest. T2 images were also generated. Visual inspection of the acquired images did not reliably distinguish increased intensity due to even-echo rephasing from the relative changes between adjacent tissues seen on second-echo images. More definitive differentiation of the even-echo phenomenon was provided by calculated values of T2 and computer-synthesized T2 images representing acquired intensity data of two-echo sequences. The synthesized images were especially useful when stationary tissue with lengthened T2 values was adjacent to or in proximity to vessels or vascular lesions. A five spin-echo image sequence was valuable for separating slow flow from stationary tissue by a technique of synthesizing T2-difference images using three consecutive echoes. 相似文献
54.
Effect of dexamethasone on symptoms of acute mountain sickness at Pikes Peak, Colorado (4,300 m) 总被引:1,自引:0,他引:1
P B Rock T S Johnson A Cymerman R L Burse L J Falk C S Fulco 《Aviation, space, and environmental medicine》1987,58(7):668-672
In a previous controlled study, dexamethasone (DEX) was shown to prevent acute mountain sickness (AMS) during exposure to simulated high altitude. To determine the effect of DEX during actual altitude exposure, 16 young men were treated with either DEX (4 mg every 6 h) or placebo for 48 h prior to and 48 h after being rapidly transported from sea level to the summit of Pikes Peak, CO (4,300 m). Symptoms of AMS were evaluated twice daily at Pikes Peak using the Environmental Symptoms Questionnaire and a clinical assessment. During treatment the mean symptom scores were higher for subjects taking placebo in 18 out of 20 comparisons. On an individual basis, 60% of the subjects receiving placebo met the criteria for being "sick" compared to 31% of subjects receiving DEX. Beginning 24 h after cessation of treatment, DEX subjects experienced a progressive increase in symptom scores which lasted through the end of the altitude sojourn (day 6). The results indicate that DEX is an effective prophylactic treatment for AMS in an actual mountain environment, but that AMS symptoms can occur if the drug is stopped abruptly. 相似文献
55.
Russell EJ; Geremia GK; Johnson CE; Huckman MS; Ramsey RG; Washburn-Bleck J; Turner DA; Norusis M 《Radiology》1987,165(3):609-617
Sixteen patients with suspected cerebral metastases were studied with magnetic resonance (MR) imaging before and after the intravenous administration of 0.1 mmol/kg of gadolinium diethylenetriaminepenta-acetic acid. The images were interpreted blindly by two neuroradiologists; all clinical, radiologic (computed tomographic and MR imaging), and pathologic data were reviewed to arrive at a final "best diagnosis," which was then compared with the prior blinded interpretations. Of seven patients found to have multiple metastases, six (86%) had at least one tumor nodule depicted by postinfusion MR imaging that was missed by one or both observers on review of preinfusion images alone. Lesions missed on preinfusion studies were usually small nodules hidden by or not detected next to regions of high-signal edema thought to be related to the adjacent tumor nodule. The authors believe that contrast enhancement improves detection of metastatic foci with MR imaging and that the findings indicate broader implications for the detection of multiple lesions from other causes. 相似文献
56.
目的:通过对骨髓单个核细胞在体外与不同细胞因子培养,了解不同细胞因子对骨髓淋巴细胞的激活能力和对骨髓干祖细胞的损伤情况。方法:将IL-1、IL-2、γ-IFN、CD3单抗进行不同组合后,在体外与骨髓单个核细胞分成对照组、IL-2组、CD3-AK、CIK组进行培养。培养过程中观察细胞形态和数量的变化,并在培养后检测免疫活性细胞的细胞毒性和造血干细胞的保存情况。结果:培养过程中对照组细胞数量减少;IL-2组细胞数量变化不明显;CD3-AK组、CIK组细胞数量显著增多,并出现较多的集聚成簇的淋巴样细胞,培养后其细胞毒性明显强于对照组及IL-2组,但细胞数量增加和细胞毒性无明性差异,培养后各组造血干细胞保存情况约16%~87%。结论:IL-2、CD3单抗在体外与骨髓单个核细胞培养后,即能激活免疫细胞增殖,又能保留足够的造血干细胞。 相似文献
57.
58.
59.
Mutations in the genome of porcine reproductive and respiratory syndrome virus responsible for the attenuation phenotype 总被引:16,自引:0,他引:16
Allende R Kutish GF Laegreid W Lu Z Lewis TL Rock DL Friesen J Galeota JA Doster AR Osorio FA 《Archives of virology》2000,145(6):1149-1161
Summary. Although live-attenuated vaccines have been used for some time to control clinical symptoms of the porcine reproductive and
respiratory syndrome (PRRS), the molecular bases for the attenuated phenotype remain unclear. We had previously determined
the genomic sequence of the pathogenic PRRSV 16244B. Limited comparisons of the structural protein coding sequence of an attenuated
vaccine strain have shown 98% homology to the pathogenic 16244B. Here we have confirmed the attenuated phenotype and determined
the genomic sequence of that attenuated PRRSV vaccine and compared it to its parental VR-2332 and the 16244B strains. The
attenuated vaccine sequence was colinear with that of the strain 16244B sequence containing no gaps and 212 substitutions
over 15,374 determined nucleotide sequence. We identified nine amino acid changes distributed in Nsp1β, Nsp2, Nsp10, ORF2,
ORF3, ORF5 and ORF6. These changes may provide the molecular bases for the observed attenuated phenotype.
Received August 28, 1999 Accepted December 16, 1999 相似文献
60.
P Rock C Beattie A W Kimball D P Nyhan B B Chen D M Fehr S A Derrer S D Parker P A Murray 《Anesthesiology》1990,73(6):1186-1197
The authors' objectives were as follows: 1) to characterize for the first time the relationship between whole body O2 delivery (DO2) and O2 consumption (VO2) in adult conscious dogs; and 2) to asses the effects of the inhalational anesthetic, halothane, on that relationship. DO2 was varied over a wide range in chronically instrumented dogs by gradual inflation and deflation of a hydraulic occluder implanted around the thoracic inferior vena cava to alter venous return and cardiac output. VO2 was measured at different values of DO2 in dogs in the fully conscious state and again during halothane anesthesia. A "binning" technique indicated that halothane decreased VO2 (P less than 0.01) at any given value of DO2 over a broad range of VO2. A two-line piecewise linear regression analysis technique indicated that halothane decreased (P less than 0.01) the critical O2 delivery (COD) from 20 +/- 3 to 10 +/- 1 ml.kg-1.min-1 and increased (P less than 0.01) O2 extraction at COD from 31 +/- 3 to 40 +/- 2%. However, the DO2-VO2 plots measured in both conscious and halothane-anesthetized dogs did not exhibit a discrete discontinuity but rather were closely fit (correlation coefficient = 0.98) by an exponential equation of the following form: O2 extraction = B1.(1 - exp (-DO2/B2))/DO2, where B1 is the delivery-independent estimate of VO2 and B2 is the "delivery constant," i.e., the DO2 associated with a VO2 equal to 63% of B1. Halothane decreased B1 (P less than 0.01) from 5.3 +/- 0.1 to 3.9 +/- 0.1 ml.kg-1.min-1 and decreased B2 (P less than 0.01) from 5.6 +/- 0.3 to 3.6 +/- 0.3 ml.kg-1.min-1 compared with that measured in conscious dogs. Thus, compared with the conscious state, halothane anesthesia alters the fundamental relationship between DO2 and VO2 and may have a beneficial effect on tissue oxygenation at low values of DO2. 相似文献