全文获取类型
收费全文 | 1978篇 |
免费 | 245篇 |
国内免费 | 1篇 |
专业分类
2224篇 |
出版年
2021年 | 23篇 |
2020年 | 34篇 |
2019年 | 54篇 |
2018年 | 49篇 |
2017年 | 23篇 |
2016年 | 41篇 |
2015年 | 46篇 |
2014年 | 67篇 |
2013年 | 85篇 |
2012年 | 101篇 |
2011年 | 101篇 |
2010年 | 68篇 |
2009年 | 58篇 |
2008年 | 92篇 |
2007年 | 79篇 |
2006年 | 90篇 |
2005年 | 55篇 |
2004年 | 60篇 |
2003年 | 60篇 |
2002年 | 70篇 |
2001年 | 72篇 |
2000年 | 57篇 |
1999年 | 60篇 |
1998年 | 32篇 |
1997年 | 35篇 |
1996年 | 31篇 |
1995年 | 43篇 |
1994年 | 21篇 |
1993年 | 30篇 |
1992年 | 48篇 |
1991年 | 32篇 |
1990年 | 48篇 |
1989年 | 54篇 |
1988年 | 42篇 |
1987年 | 40篇 |
1986年 | 18篇 |
1985年 | 21篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1980年 | 18篇 |
1979年 | 15篇 |
1978年 | 24篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1973年 | 14篇 |
1972年 | 13篇 |
1971年 | 15篇 |
1968年 | 11篇 |
排序方式: 共有2224条查询结果,搜索用时 0 毫秒
1.
2.
A case of chromomycosis in which hyperthermia proved effective is reported. The patient was a 56-year-old male bean curd maker who, without any previous history of minor trauma, developed on the extensor side of the left upper arm an eczematous lesion that underwent gradual radial expansion. The lesion showed a well-defined, 7×10 cm infiltrated erythematous plaque with the central area healed and, at the upper and lower borders, adherent scales and crusts on the surface. Histological examination revealed granulomatous changes in the dermis, as well as sclerotic cells within giant cells and microabscesses. On culturing,Fonsecaea pedrosoi was isolated. The patient was treated with disposable chemical pocket warmers, which were secured over the lesion with a rather tight elastic bandage, so that they kept the affected area warm for 24 hours a day. After a month of such hyperthermic treatment, the erythema and infiltration had decreased considerably, and microscopic examination and culture of the crusts both yielded negative results. Examination of biopsy specimens of the lesion after the third month showed that it had cicatrized. The treatment was stopped after 4 months, and no relapse occurred. We also summarize the published results of local hyperthermic treatment of chromomycosis in Japan. 相似文献
3.
Influence of paternally imprinted genes on development. 总被引:4,自引:0,他引:4
S C Barton A C Ferguson-Smith R Fundele M A Surani 《Development (Cambridge, England)》1991,113(2):679-687
The parental origin of chromosomes is critical for normal development in the mouse because some genes are imprinted resulting in a predetermined preferential expression of one of the alleles. Duplication of the paternal (AG: androgenones) or maternal (GG/PG: gynogenones/parthenogenones) genomes will result in an excess or deficiency of gene dosage with corresponding phenotypic effects. Here, we report on the effects of paternally imprinted genes on development following introduction of the AG inner cell mass into normal blastocysts. There was a striking increase in embryonic growth by up to 50%, and a characteristic change in embryonic shape, partly because of the corresponding increase in length of the anterior-posterior axis. These changes, between e12-e15, were proportional to the contribution from AG cells to the embryo. However, a contribution of AG cells in excess of 50% was invariably lethal as development progressed to e15. A limited number of chimeras were capable of full-term development provided there was a relatively low contribution from AG cells. The distribution of AG cells in chimeras was not uniform, especially later in development when there was a disproportionate presence of AG cells in the mesodermally derived tissues. Their contribution was consistently greater in the heart and skeletal muscle, but was considerably lower in the brain. Chimeras detected after birth were either dead or developed severe abnormalities of the skeletal elements, particularly of the ribs which were enlarged, distorted and fused, with greatly increased cartilaginous material with an absence of normal ossification. These phenotypic effects in chimeras are reciprocal to those observed in the presence of GG/PG cells, which resulted in a substantial size reduction approaching 50%.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
4.
The thymic microenvironment. Characterization of in vitro differentiation of the IT26R21 rat thymic epithelial cell line 总被引:3,自引:0,他引:3
David F. Lobach Tsunetoshi Itoh Kay H. Singer Barton F. Haynes 《Differentiation; research in biological diversity》1987,34(1):50-59
We have previously postulated an in vivo pathway of thymic epithelial (TE) cell maturation in pre- and postnatal thymus, whereby endocrine medullary TE cells terminally differentiate to form Hassall's bodies. Epithelial-cell differentiation has been well documented in vitro using epidermal keratinocytes. Therefore, to characterize TE-cell differentiation in vitro, we observed clones of the rat TE cell line, IT26R21, after 4 and 14 days in culture. We found alterations in cell morphology, the cessation of cell proliferation, and the acquisition of a differentiation antigen defined by monoclonal antibody TE-19 (a marker of terminally differentiated epithelial cells). At light and electron microscopy, we detected progressive TE-cell stratification and squamous-cell formation between 4 and 14 days of culture. Autoradiography on day 14 showed that squamous TE cells in stratified layers did not incorporate tritiated thymidine, while surrounding smaller cells adhering to the substratum continued to synthesize DNA. At indirect immunofluorescence, only 3% of cells reacted with monoclonal antibody TE-19 at day 4, while on day 14, 22% of the TE cells were TE-19 positive (P less than 0.02). Antibody-TE-19 reactivity was limited to stratified, squamous TE cells. Additionally, we isolated a clone of the IT26R21 cell line that did not undergo these changes characteristic of TE cell differentiation. We conclude that IT26R21 TE cells are capable of undergoing programs of both terminal differentiation and cell renewal in vitro. 相似文献
5.
6.
7.
Adult Antarctic fur seals (Arctocephalus gazella) were immobilized with Zoletil® ( n = 172), ketamine ( n = 30), ketamine mixed with diazepam ( n = 23) and with ketamine mixed with xylazine ( n = 45). Response to all drugs was highly variable. There was a relationship between dose rate and level of immobilization in females given Zoletil® . Males were slightly more sensitive to Zoletil® than females but this could have been due to the greater body mass and lower mass-specific metabolic rate of males. The dose required to achieve a level of immobilization declined with greater body mass for Zoletil® and ketamine but not for ketamine-diatepam. Ketamine and ketamine-sedative mixtures commonly caused mild tremoring and occasionally caused convulsions. Neither reaction was seen with Zoletil® . Mean doses were, Zoletil® 1.5 mg/ kg, ketamine 6.9 mg/kg, ketamine-diazepam 6.3 mg/kg ketamine and 6.3 μg/kg diazepam, and ketamine-xylazine 7.3 mg/kg ketamine and 0.62 mg/ kg xylazine. Zoletil® performs at least as well on Antarctic fur seals as ketamine but it may cause respiratory depression. The dose of ketamine required for Antarctic fur seals was greater than for most other species of seals. 相似文献
8.
H. Barton Grossman Gary Wedemeyer Judith Stein 《Cancer immunology, immunotherapy : CII》1988,26(3):269-272
Summary The autologous serologic reactivity of 13 patients with bladder cancer was evaluated using cell lines derived from each individual's own tumor as targets. Protein A and immune adherence assays were employed to determine antibody binding to the tumor targets at varying passage numbers. Autologous reactivity was found in 6 of the 13 cell lines tested. However, the titer was usually low regardless of the passage number. Seven autologous serum/cell line combinations were tested using both low and high passage cells as targets. In six of these combinations, the degree of antibody binding was similar with both low and high passage target cells. The incidence of autologous reactivity in the 12 patients with urothelial tumors was 50%.This investigation was supported by PHS Grant number CA36933, awarded by the National Cancer Institute, DHHS. 相似文献
9.
A number of different membrane associated isoforms of the neural cell adhesion molecule (N-CAM) have previously been identified. Here the structure of a novel secreted isoform of N-CAM is established by analysis of a cDNA corresponding to an N-CAM mRNA from human skeletal muscle. The mRNA incorporates a novel sequence block into the extracellular domain, which introduces an in-frame stop codon and thus prematurely terminates the coding sequence, generating a truncated N-CAM polypeptide. Analysis of genomic clones indicates that the inserted sequence is present as a discrete exon within the human N-CAM gene, and Northern analysis shows it to be associated specifically with a 5.2 kb mRNA species from skeletal muscle and brain. Stable transfectants expressing the secreted isoform accumulate it in the cytoplasm and release it to the culture medium. In contrast, cells transfected with cDNA encoding lipid-tailed N-CAM express it predominantly at the cell surface. The existence of a secreted isoform may further expand the spectrum of N-CAM function beyond its known involvement in intercellular adhesion to extracellular matrix interactions. 相似文献
10.
Novel biotransformations of 4-chlorobiphenyl by a Pseudomonas sp 总被引:7,自引:0,他引:7
A bacterium, tentatively identified as a representative of the genus Pseudomonas (strain MB86), was isolated from soil contaminated by wood-preservation chemicals by using 4-chlorobenzoate as an enrichment substrate. The pseudomonad was able to grow on 4-chlorobenzoic acid and 4-chlorobiphenyl as sole carbon and energy sources. Spent culture medium from 4-chlorobiphenyl-grown cells contained 4-chlorobenzoic acid, 4'-chloroacetophenone, 2-hydroxy,2-[4'-chlorophenyl] ethane, and 2-oxo,2-[4'-chlorophenyl] ethanol as metabolites. 4'-Chloroacetophenone was produced in large amounts, possibly as a dead-end metabolite. 相似文献