全文获取类型
收费全文 | 6129篇 |
免费 | 556篇 |
国内免费 | 120篇 |
专业分类
耳鼻咽喉 | 52篇 |
儿科学 | 182篇 |
妇产科学 | 103篇 |
基础医学 | 991篇 |
口腔科学 | 185篇 |
临床医学 | 826篇 |
内科学 | 993篇 |
皮肤病学 | 120篇 |
神经病学 | 383篇 |
特种医学 | 537篇 |
外国民族医学 | 1篇 |
外科学 | 799篇 |
综合类 | 140篇 |
一般理论 | 6篇 |
预防医学 | 619篇 |
眼科学 | 88篇 |
药学 | 433篇 |
中国医学 | 2篇 |
肿瘤学 | 345篇 |
出版年
2021年 | 66篇 |
2019年 | 65篇 |
2018年 | 95篇 |
2017年 | 53篇 |
2016年 | 78篇 |
2015年 | 85篇 |
2014年 | 126篇 |
2013年 | 188篇 |
2012年 | 189篇 |
2011年 | 255篇 |
2010年 | 162篇 |
2009年 | 153篇 |
2008年 | 205篇 |
2007年 | 309篇 |
2006年 | 215篇 |
2005年 | 233篇 |
2004年 | 203篇 |
2003年 | 186篇 |
2002年 | 182篇 |
2001年 | 205篇 |
2000年 | 214篇 |
1999年 | 163篇 |
1998年 | 154篇 |
1997年 | 143篇 |
1996年 | 161篇 |
1995年 | 107篇 |
1994年 | 103篇 |
1993年 | 98篇 |
1992年 | 104篇 |
1991年 | 142篇 |
1990年 | 127篇 |
1989年 | 147篇 |
1988年 | 128篇 |
1987年 | 156篇 |
1986年 | 111篇 |
1985年 | 124篇 |
1984年 | 102篇 |
1983年 | 81篇 |
1982年 | 69篇 |
1981年 | 57篇 |
1980年 | 75篇 |
1979年 | 69篇 |
1978年 | 66篇 |
1977年 | 75篇 |
1976年 | 70篇 |
1975年 | 68篇 |
1974年 | 49篇 |
1973年 | 64篇 |
1971年 | 49篇 |
1970年 | 44篇 |
排序方式: 共有6805条查询结果,搜索用时 0 毫秒
51.
Claire M. Payne Raymond B. Nagle Samuel H. Paplanus Anna R. Graham Martin M. Berman 《Ultrastructural pathology》1986,10(6):539-552
Immunohistochemical and ultrastructural findings in two cases of fibrolamellar carcinoma of the liver and two cases of hepatocellular carcinoma of the common histologic type are described. Ultrastructural examination of both cases of fibrolamellar carcinoma revealed the presence of neurosecretory (NS) granules which were sparse in some cells and abundant in others. Many of the tumor cells had a distinct oncocytic appearance with abundant mitochondria. A portion of the glutaraldehyde-fixed neoplasm was processed for the uranaffin reaction (an ultrastructural cytochemical stain specific for the NS granules of neuroendocrine tissue). Abundant uranaffin-positive granules were found in the neoplastic cells of both cases of fibrolamellar carcinoma, whereas no uranaffin-positive granules were found in hepatocellular carcinoma of the common histologic type. There was no statistical difference in the mean diameter of the uranaffin-positive granules measured from both cases. Immunohisto-chemistry revealed the presence of neuron-specific enolase (NSE) and serotonin in one of the two cases of fibrolamellar carcinoma and no NSE staining in two cases of hepatocellular carcinoma of the common histologic type. These findings suggest that some liver tumors presenting histologically as fibrolamellar carcinoma may be neuroendocrine in nature. 相似文献
52.
Mnemonic coding system for clinical data entry into laboratory computers: its effect on quality and efficiency. 下载免费PDF全文
I R Bailey K B Page R G Jones R B Payne A J Little 《Journal of clinical pathology》1991,44(12):1018-1021
A simplified coding method for entering the clinical details found on pathology request cards was developed. The method uses a basic four letter code, derived from the initial character of the first four words in a clinical detail, being expanded to four characters with letters from the final word if the number of words is less than four. Rules were devised to cope with common medical terminology. In excess of 90% of clinical details on request cards are readily input by clerical staff using our coding system, and 8% of clinical details are used intelligently by the computer in scheduling further tests or automatically commenting on results. A carefully designed coding system such as the one outlined above could greatly facilitate input of clinical detail without the penalty of reduced throughput. 相似文献
53.
54.
The polypeptide composition of vaccinia-infected cell membranes and rifampicin bodies 总被引:1,自引:0,他引:1
The protein and glycoprotein composition of a sucrose gradient fraction from vaccinia infected cells treated with rifampicin was studied. This particulate fraction contained cytoplasmic membranes and pleomorphic membranous structures. The glycoproteins (89, 42 and 20-23 kDa, respectively) were identified as the same glycoproteins that are found in plasma membranes of infected cells and the envelope of extracellular enveloped vaccinia (EEV). These glycoproteins could be solubilized by 0.1% NP-40. The Golgi membrane associated 41K acylated vaccinia protein was also NP-40 soluble. In contrast, most particulate fraction proteins (125, 100, 86, 65, 41, 39, 31, 27, 25, 14 and 12.5 kDa) with the exception of the 33 and 29 kDa proteins remained essentially insoluble after NP-40 treatment. The 86 and 65 kDa proteins are the rifampicin inhibited precursors to INV core proteins while the 33 and 29 kDa proteins are INV surface proteins. Twelve proteins behaved like their respective comigrating INV proteins when extracted with NP-40 and 2ME. Electron microscopy showed that a centrifuged sediment from NP-40 treated cells contained pleomorphic protein containing membranous structures that we have called rifampicin bodies. We conclude that (1) the major glycoproteins found in the particulate fraction from sucrose gradients are vaccinia glycoproteins residing in cytoplasmic membranes while (2) the major non-glycosylated proteins are components of the rifampicin bodies and that (3) the rifampicin bodies represent an intermediate in the morphogenetic process leading to mature INV. 相似文献
55.
Lomber SG Payne BR Hilgetag CC Rushmore J 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2002,142(4):463-474
A contralateral hemineglect of the visual field can be induced by unilateral cooling deactivation of posterior middle suprasylvian (pMS) sulcal cortex of the posterior parietal region, and this neglect can be reversed by additional cooling deactivation of pMS cortex in the opposite hemisphere. The purpose of the present study was to test whether an enduring hemianopia induced by removal of all contiguous visual cortical areas of one hemisphere could be reversed by local cooling of pMS cortex in the opposite hemisphere. Two cats sustained large unilateral ablations of the contiguous visual areas, and cooling loops were placed in the pMS sulcus, and in contact with adjacent area 7 or posterior ectosylvian (PE) cortex of the opposite hemisphere. In both instances cooling of pMS cortex, but neither area 7 nor PE, restored a virtually normal level of orienting performance to stimuli presented anywhere in the previously hemianopic field. The reversal was highly sensitive to the extent of cooling deactivation. In a third cat, cooling deactivation of the superficial layers of the contralateral superior colliculus also restored orienting performance to a cortical ablation-induced hemianopia. This reversal was graded from center-to-periphery in a temperature-dependent manner. Neither the cortical ablation nor any of the cooling deactivations had any impact on an auditory detection and orienting task. The deactivations were localized and confirmed by reduced uptake of radiolabeled 2-deoxyglucose to be limited to the immediate vicinity of each cooling loop. The results are discussed in terms of excitation and disinhibition of visual circuits. 相似文献
56.
The sciatic nerve was crushed in the right hindlimb in newborn (3-8 h old) rats. Two to four months later, electromyographic activity was recorded from both the control and reinnervated ankle extensor muscles soleus or lateral gastrocnemius and from the ankle flexor muscle tibialis anterior. Tonic postural activity was present in the extensor muscles on both sides during quiet stance. The control flexor muscles were usually silent in this situation, but the reinnervated flexors exhibited abnormal sustained activity. During locomotion, the control extensors were activated during the stance phase and their mean burst made up 61.5% of the step cycle. The control tibialis anterior muscle fired only during the swing phase, with the burst lasting 18.1% of the step cycle. In the reinnervated extensor muscles, the mean burst duration was decreased (46% of the cycle) but the basic locomotor pattern was not impaired. The reinnervated tibialis muscle, however, was activated abnormally, with one appropriate flexor burst during the swing phase and an "extensor-like" burst during the stance phase of the step. Reflex responses to stretch were weak or absent on the operated side. Histological examination showed that the reinnervated soleus and tibialis muscles were almost devoid of muscle spindles. The motor unit mean firing rates in the reinnervated soleus (22 imp/s) and lateral gastrocnemius (45 imp/s) matched those of the control muscles (25 and 42 imp/s, respectively). In contrast to the phasic, high-frequency firing (52-80 imp/s) in the control tibialis, the reinnervated tibialis motor units fired at significantly lower rates (22-56 imp/s).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
57.
The properties of three baculoviruses from closely related hosts. 总被引:15,自引:0,他引:15
The baculoviruses of three important and closely related pest insects, Spodoptera littoralis, S. exempta and S. frugiperda, were purified and several of their properties were compared. These include data on virus morphology, physical properties of the virus particle, serological properties, structural polypeptides, and viral DNA. The effect of the endogenous polyhedron alkaline protease on the polyhedron and virus particle proteins was also investigated. Biochemical and biophysical differences between the viruses were found which were reflected in their serological properties. The feasibility of using a simple serological technique for specific identification of each virus has been demonstrated. 相似文献
58.
Michael Rossdale Terry Kemple Sarah Payne Michael Calnan Rosemary Greenwood 《The British journal of general practice》2007,57(535):152-154
Out-of-hours organisations are responsible for the care of patients 70% of the time, and their GPs act as gatekeepers to secondary care services. This observational study identifies the variations in GPs' out-of-hours referral rates to secondary care and factors that could explain these variations. One hundred and forty-nine GPs who worked in one UK general practice out-of-hours cooperative which served 19 practices with 167 000 registered patients. Data on patients who accessed the out-of-hours service over 3 years (2001-2004) were examined. Factors thought to be predictors of variation in referral rates were investigated using logistic regression analysis. There was a fivefold difference in referral rates between the lowest and highest referring quartiles of GPs (OR [odds ratio] = 4.56, CI [confidence interval] = 3.86 to 5.38). The sex (female) of the clinician, the time of the consultation (11 pm to 7 am), and the place of the consultation (home visit) accounted for some, but not all, of the increased referral rates. A doctor working out-of-hours disproportionately influences the fate of the patient, the number of hospital admissions, and extra costs to the health service. There is a need for follow-up studies to investigate the factors associated with referral behaviour, and how the variation relates to patient factors and the resources available. These findings could be used when planning the staffing of out-of-hours services to optimise appropriate care and minimise patients' exposure to unnecessary intrusive and expensive hospital care. 相似文献
59.
Regulation of iron uptake and utilization is critical for bacterial growth and for prevention of iron toxicity. In many bacterial species, this regulation depends on the iron-responsive master regulator Fur. In this study we report the effects of iron and Fur on gene expression in Vibrio cholerae. We show that Fur has both positive and negative regulatory functions, and we demonstrate Fur-independent regulation of gene expression by iron. Nearly all of the known iron acquisition genes were repressed by Fur under iron-replete conditions. In addition, genes for two newly identified iron transport systems, Feo and Fbp, were found to be negatively regulated by iron and Fur. Other genes identified in this study as being induced in low iron and in the fur mutant include those encoding superoxide dismutase (sodA), fumarate dehydratase (fumC), bacterioferritin (bfr), bacterioferritin-associated ferredoxin (bfd), and multiple genes of unknown function. Several genes encoding iron-containing proteins were repressed in low iron and in the fur mutant, possibly reflecting the need to reserve available iron for the most critical functions. Also repressed in the fur mutant, but independently of iron, were genes located in the V. cholerae pathogenicity island, encoding the toxin-coregulated pilus (TCP), and genes within the V. cholerae mega-integron. The fur mutant exhibited very weak autoagglutination, indicating a possible defect in expression or assembly of the TCP, a major virulence factor of V. cholerae. Consistent with this observation, the fur mutant competed poorly with its wild-type parental strain for colonization of the infant mouse gut. 相似文献
60.
Iron-vibriobactin transport system is not required for virulence of Vibrio cholerae. 总被引:8,自引:6,他引:8 下载免费PDF全文
The possible requirement of a functional siderophore (vibriobactin)-mediated iron transport system in the pathogenicity of Vibrio cholerae was determined. Two mutants of V. cholerae defective in the iron-vibriobactin transport system were examined for their ability to multiply and elicit diarrhea in infant mice. One mutant, 40130, was unable to synthesize vibriobactin. The second mutant, 1510, was able to synthesize, but not transport, the siderophore. Both mutants retained the ability to multiply and produce disease in the infant mouse, and virulence was indistinguishable from the parent strains. This indicates that a functional iron-vibriobactin transport system is not essential for cholera pathogenesis. These mutants, like the wild-type strains, were found to have a ferric citrate iron uptake system and could utilize citrate or asparagine for growth in low-iron medium. Compounds of this type may increase the availability of iron to V. cholerae in the host. 相似文献