全文获取类型
收费全文 | 14507篇 |
免费 | 1184篇 |
国内免费 | 60篇 |
专业分类
15751篇 |
出版年
2023年 | 134篇 |
2022年 | 94篇 |
2021年 | 226篇 |
2020年 | 192篇 |
2019年 | 181篇 |
2018年 | 447篇 |
2017年 | 433篇 |
2016年 | 406篇 |
2015年 | 351篇 |
2014年 | 411篇 |
2013年 | 725篇 |
2012年 | 1192篇 |
2011年 | 1301篇 |
2010年 | 632篇 |
2009年 | 450篇 |
2008年 | 1090篇 |
2007年 | 1101篇 |
2006年 | 1058篇 |
2005年 | 943篇 |
2004年 | 934篇 |
2003年 | 886篇 |
2002年 | 760篇 |
2001年 | 161篇 |
2000年 | 232篇 |
1999年 | 135篇 |
1998年 | 107篇 |
1997年 | 76篇 |
1996年 | 64篇 |
1995年 | 77篇 |
1994年 | 66篇 |
1993年 | 57篇 |
1992年 | 69篇 |
1991年 | 60篇 |
1990年 | 50篇 |
1989年 | 38篇 |
1988年 | 37篇 |
1987年 | 36篇 |
1986年 | 25篇 |
1985年 | 31篇 |
1984年 | 50篇 |
1983年 | 30篇 |
1982年 | 47篇 |
1981年 | 43篇 |
1980年 | 50篇 |
1979年 | 32篇 |
1978年 | 34篇 |
1977年 | 30篇 |
1976年 | 31篇 |
1975年 | 30篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Maria Manuela M. Caniça Chang Y. Lu Rajagopal Krishnamoorthy Gérard C. Paul 《Journal of molecular evolution》1997,44(1):57-65
The molecular diversity of inhibitor-resistant TEM (IRT) enzymes was explored using a strategy which involved DNA amplification
by polymerase chain reaction (PCR), analysis of restriction fragment length polymorphism (RFLP), and direct nucleotide sequencing.
The study of plasmid-borne genes from 27 strains, resistant to amoxicillin and β-lactamase-inhibitor combinations, identified
mutations resulting in amino acid change at positions 69, 244, 275, and 276 known to be associated with the IRT phenotype
and a mutation at nucleotide position 162 in the promoter region. These mutations were found to lie on two different gene
sequences, described here as ``TEM-1B like' and ``TEM-2 like' restriction linkage groups. Further analysis, of nucleotide
sequences of promoter and coding regions of the β-lactamases, confirmed that a given mutation causing IRT phenotype could
be associated with two different gene sequence frameworks and two different causal mutations could lie on identical gene sequence
framework. These data argue in favor of convergent phenotypic evolution of IRT enzymes under the selective pressure imposed
by the intensive clinical use of β-lactam–β-lactamase inhibitor combinations.
Received: 18 March 1996 / Accepted: 15 July 1996 相似文献
72.
M. L. Kottler F. Lorenzo F. Bergametti P. Commerçon C. Souchier R. Counis 《Human genetics》1995,96(4):477-480
We have isolated nine yeast artificial chromosomes (YACs) containing the gene that encodes the human gonadotropin-releasing hormone receptor (GnRH-R) gene by screening the YAC library of the Centre d'Etude du Polymorphisme Humain (Hôpital Saint-Louis, Paris, France) by the use of the polymerase chain reaction. We defined the location of the GnRH-R gene relative to 4q microsatellite markers D4S392 and D4S409. The genetic positions of these markers on chromosome 4 are 76 and 77 cM, respectively. This location was further established by chromosomal in situ hybridization. 相似文献
73.
Suzanne Demczuk Annie Lévy Muriel Aubry Marie-Françoise Croquette Nicole Philip Marguerite Prieur Ursula Sauer Patrice Bouvagnet Guy A. Rouleau Gilles Thomas Alain Aurias 《Human genetics》1995,96(1):9-13
We have determined the parental origin of the deleted chromosome 22 in 29 cases of DiGeorge syndrome (DGS) using a CA-repeat mapping within the commonly deleted region, and in one other case by using a chromosome 22 short arm heteromorphism. The CA-repeat was informative in 21 out of 29 families studied and the deleted chromosome was of maternal origin in 16 cases (72%). When these data are pooled with recent results from the literature, 24 de novo DGS, velo-cardio-facial syndrome (VCFS) and isolated conotruncal cardiac disease deletions are found to be of maternal origin and 8 of paternal origin, yielding a 2 of 8 with a probability level lower than 0.01. These data, and review of the literature on familial DGS/VCFS and isolated conotruncal cardiopathies suggest that there is a strong tendency for the 22q11.2 deletions to be of maternal origin. 相似文献
74.
Cells of Escherichia coli induced for l-tryptophan synthase [l-serine hydro-lyase (adding indole-glycerol-phosphate), EC 4.2.1.20] have been assayed in DMF and DMSO aqueous solvents as reaction medium. Up to 20% DMF/water, cells retained 90% of their tryptophan synthase activity. Concentrations of 20 mM indole, which did not inhibit this reactivity, could be reached with 5% DMF/water. Four matrices were compared for cell immobilization: polyacrylamide, foam particles of bovine seum albumin, alginate and κ-carrageenan. The best activity was retained with the latter matrix, and the preparations thus obtained allowed high productivity of l-tryptophan. Various systems of production of l-tryptophan with κ-carrageenan and DMF/water were studied. 相似文献
75.
Pierre-François Piguet 《Immunogenetics》1984,20(1):71-81
A systemic graft-versus-host reaction (GVHR) leading to 50% mortality by day 20 was elicited by the injection of CBA (105) or B10 (106) parental T lymphocytes into irradiated (750 rad) and bone marrow protected (CBA x B10)F1 recipients. Between days 12 and 28 the spleens of the sick mice were analyzed by limiting dilution, performed with irradiated F1 cells and a source of interleukin-2 (IL-2), to determine the frequency of cells with an antihost proliferative or cytolytic activity and to derive T lymphocyte clones. The frequency of cells with antihost proliferative or cytolytic activity was approximately 10–3 in either combination. In the CBA vs F1 GVHR, all eight clones isolated with anti-F1 activity were Lyt-2–, noncytolytic, mixed lymphocyte reaction (MLR) responders and IL-2 producers, three of which mapped to the A
b
locus, while in the B10 anti-F1 combination, eight of the nine anti-F1 clones isolated were Lyt-2+, poor MLR responders and non-IL-2 producers, but cytolytic and mapping to K
k
. These findings suggest a much higher frequency of T cells recognizing the A-locus antigens in the CBA than in the B10 strain. 相似文献
76.
Françoise Dacheux 《Cell and tissue research》1984,235(3):615-621
Summary The aim of the present study on the fetal porcine pituitary was (1) to detect by means of the immunoperoxidase technique the earliest stages of cells producing polypeptide hormones: -MSH, ACTH, -LPH, - and -endorphin, growth hormone (GH) and prolactin (PRL), (2) to study the development of the synthesis and the storage of these hormones during fetal life, and (3) to detect whether several hormones can be located in one and the same cell.The corticotropic cells were revealed as the earliest functional elements of the fetal anterior pituitary. Our results indicate clearly that ACTH, -MSH, -LPH, - and -endorphin appear at 34 days in the same regular, round or ovoid cells; no differences in the time of their appearance could be observed. The ACTH-cells, irregular or angular in shape and endowed with cytoplasmic processes such as described in the adult pituitary, were not seen until day 50. The first GH-cells were detected between 40 to 45 days of fetal life. From day 45 to 90, the GH-cells greatly increased in number and in staining intensity of their progressively extending cytoplasmic area, but they displayed the same regular and round shape. The PRL-cells were the last cell type to appear in the fetal pituitary. The first PRL-cells, small in size and round or ovoid in shape with a high nucleus/cytoplasm ratio, were detected at day 70. At day 80, the PRL-cells increased in size and staining intensity. They displayed an irregular elongated or stellated shape and cytoplasmic processes resembling those characteristic of the adult pituitary. These data suggest that in the fetal porcine pituitary: (1) ACTH, -LPH and related peptides are synthesized and stored in the same cells, and (2) PRL and GH appear in individual cellular elements. 相似文献
77.
Del11p13/nephroblastoma without aniridia 总被引:6,自引:0,他引:6
Catherine Turleau J. de Grouchy Claire Nihoul-Fékété J. L. Dufier Françoise Chavin-Colin Claudine Junien 《Human genetics》1984,67(4):455-456
Summary A patient is reported with del11p13, low catalase level, nephroblastoma, chordee and cryptorchidism, no evident mental retardation, and with normal irides. This unique observation suggests the following order of loci in 11p13, from centromere to telomere: catalase, Wilms tumor, aniridia. The chromosomal origin of nephroblastoma may be more frequent than estimated on the basis of its association with aniridia. 相似文献
78.
Summary Observations in a family point to the existence of autosomal dominant inheritance for discrete subaortic stenosis (DSS), which made up part of a multisystem disorder. Both parents, offspring of two full siblings, had short stature, obstructive lung disease (OLD), hoarseness and upturned nose. The father alone had aortic stenosis and inguinal hernia.The six offspring, aged from 13 to 28 years, were followed up for up to 8 years. While one of them was virtually normal, and one had only minor abnormalities, four siblings displayed clinical signs of progressive aortic stenosis. Of the two eldest siblings who eventually died, necropsy in one showed a discrete subaortic stenosis, which was hemodynamically proven in one and surgically corrected in another sibling.Upturned nose was present in each examined member of the family, short stature and hoarseness in five of the siblings, DSS in four, OLD, inguinal hernia and congested episcleral veins in three, kyphoscoliosis in two, while epicanthus, strabismus, microphthalmos and widely spaced teeth were noted in the deceased female. The prevalence of some of these traits in roughly three-quarters of the sibship was consistent with an underlying single gene abnormality in affected heterozygous parents. We proposed that this constitutes a new syndrome. 相似文献
79.
80.
Summary A microcalorimetric study is proposed to follow the degradation of straw by a mixed bacterial culture. The effect of an alkali pretreatment of straw is described. 相似文献