全文获取类型
收费全文 | 9607篇 |
免费 | 542篇 |
专业分类
10149篇 |
出版年
2022年 | 55篇 |
2021年 | 102篇 |
2020年 | 55篇 |
2019年 | 76篇 |
2018年 | 110篇 |
2017年 | 104篇 |
2016年 | 179篇 |
2015年 | 254篇 |
2014年 | 282篇 |
2013年 | 538篇 |
2012年 | 454篇 |
2011年 | 469篇 |
2010年 | 277篇 |
2009年 | 295篇 |
2008年 | 441篇 |
2007年 | 433篇 |
2006年 | 382篇 |
2005年 | 422篇 |
2004年 | 397篇 |
2003年 | 398篇 |
2002年 | 384篇 |
2001年 | 357篇 |
2000年 | 380篇 |
1999年 | 276篇 |
1998年 | 123篇 |
1997年 | 90篇 |
1996年 | 67篇 |
1995年 | 77篇 |
1994年 | 74篇 |
1993年 | 84篇 |
1992年 | 201篇 |
1991年 | 199篇 |
1990年 | 201篇 |
1989年 | 192篇 |
1988年 | 176篇 |
1987年 | 144篇 |
1986年 | 118篇 |
1985年 | 112篇 |
1984年 | 110篇 |
1983年 | 87篇 |
1982年 | 76篇 |
1981年 | 65篇 |
1979年 | 87篇 |
1978年 | 64篇 |
1977年 | 64篇 |
1976年 | 58篇 |
1975年 | 60篇 |
1974年 | 58篇 |
1973年 | 55篇 |
1972年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
H Nakamura M Koga S Higa B Sato K Noma Y Morimoto S Kishimoto E Nakano T Sonoda 《Endocrinologia japonica》1987,34(4):545-551
A 58-year-old woman was admitted to our hospital complaining of headache, dizziness and intermittent elevation of blood pressure. Multiple café-au-lait spots and neurofibromas had appeared on the back and the limbs since the age of 30 years. At the age of 54 years she underwent total thyroidectomy because of papillary carcinoma of the thyroid gland. On admission, the levels of plasma norepinephrine and epinephrine, urinary norepinephrine and normetanephrine were all within the normal range. However, urinary excretion of metanephrine was markedly increased to 1.49 +/- 0.45 (Mean +/- SD) mg/day and that of epinephrine was also slightly increased. The computed tomographic scans of the abdomen and the scintigraphy with 131I-metaiodobenzylguanidine revealed a tumor mass in the region of the right adrenal gland. The tumor was histologically confirmed to be pheochromocytoma at the operation. In her family history, her mother and one of her two sisters had von Recklinghausen's disease and another sister suffered from follicular carcinoma of the thyroid gland. As far as we know, this paper is the first report of a patient with von Recklinghausen's disease associated with both pheochromocytoma and non-medullary carcinoma of the thyroid gland, and her family. 相似文献
32.
Homoeosis in Drosophila: The Lethal Syndrome of the Regulator of bithorax (or trithorax) Locus and Its Interaction with Other Homoeotic Loci 总被引:4,自引:1,他引:3 下载免费PDF全文
Regulator of bithorax (Rg-bx)- [or trithorax (trx)-] lethal zygotes show anterior transformations of various cuticular features of the larval thorax and abdomen. The Rg-bx- lethal syndrome depends on the dosage of the bithorax gene complex (BX-C), and lack of Rg-bx+ function is antagonistic to posterior transformations displayed by Polycomb ( Pc)- embryos. Significantly, when the BX-C is deleted, the Rg-bx- embryos disclose homoeosis of mesothoracic to prothoracic cuticular structures. This homoeotic transformation is due to a reduction in Antennapedia (Antp)+ gene activity and is consequently dependent on the dosage of the Antennapedia gene complex (ANT-C), suggesting that the Rg-bx+ activity is necessary for proper expression of the Antp+ gene. However, the functional relationship between the Rg-bx and Sex combs reduced (Scr) loci in embryogenesis is still to be established. 相似文献
33.
The photosynthetic characteristics of photoautotrophically culturedcells of tobacco (Nicotiana tabacum cv. Samsun NN) as well asthose of photomixotrophically cultured cells and green leaveswere investigated. Analyses revealed that on a fresh weightbasis cultured tobacco cells had lower chlorophyll contentsthan cells of green leaves. The chlorophyll content per chloro-plast,however, was almost the same in both types of cell, and thechloroplast number per cell accounted for only small differencesin the cellular chlorophyll content. This indicates that thelarger cell volume of cultured cells is the main factor in thedifference in the chlorophyll content of these cells. Photosynthetic activity measurements also showed differencesin the chloroplasts of cultured and leaf cells. The maximumactivities of photosystem I and the Hill reaction for the culturedcells were about half those for leaf cells on a per unit chlorophyllbasis. Moreover, photo-autotrophic cells had relatively constantphotosystem I and Hill reaction activities during growth; whereas,on a fresh weight basis these activities in leaf cells reflecteddevelopmental changes in the chlorophyll content. Lithium dodecyl sulfate-polyacrylamide gel electrophoresis showedqualitatively similar thylakoid polypeptide compositions forcultured and leaf cells at all stages of growth even thoughthere were quantitative decreases in the contents of severalpolypeptides in the cultured green cells (especially in photomixotrophiccells) in comparison to the polypeptide contents of tobaccoleaves. We speculate that the lower photosynthetic activityof the cultured cells may be caused by this reduction in thecontents of certain thylakoid polypeptides. (Received November 14, 1988; Accepted June 19, 1989) 相似文献
34.
Yoshinao Nakagawa Manabu Totsuka Tomoaki Sato Yoshiro Fukuda Koichi Hirota 《European journal of applied physiology and occupational physiology》1989,59(3):239-242
We examined the influence exerted, through disuse of the hindlimb, on the collagen fibres of the achilles tendon in rats. With disuse the body mass decreased by 28%, and the mass of soleus muscle decreased by 20%. A decrease in the surface area and diameter was observed in the experimental group when compared to the control group. A histogram of the collagen fibres showed a decrease of the thick fibres in the experimental group. The maximum surface area of collagen fibres in the experimental group was seen to be only 43% of that of the control group. These results showed a decrease in the thickness of the collagen fibres of the achilles tendon through disuse. This seemed to suggest that resistance to tension is decreased by disuse. 相似文献
35.
Summary The Catecholaminergic innervation of neurons containing growth hormone-releasing factor (GRF) was examined by use of a method which combined either 5-hydroxydopamine (5-OHDA) uptake or autoradiography after intraventricular injection of 3H-noradrenaline with immunocytochemistry for GRF in the same tissue sections at the electron-microscopic level. In the ventrolateral part of the arcuate nucleus of the rat hypothalamus a large number of immunonegative axon terminals were found to make synaptic contact with GRF-like immunoreactive (GRF-LI) cell bodies and processes. 3H-noradrenaline autoradiography or 5-OHDA-labeling combined with GRF immunocytochemistry revealed that axon terminals labeled with 3H-noradrenaline or 5-OHDA make synaptic contact with the GRF-LI nerve cell bodies and processes. These findings indicate that catecholamine-containing neurons innervate GRF neurons to regulate GRF secretion via synapses in the rat arcuate nucleus. 相似文献
36.
IS421, a new insertion sequence in Escherichia coli 总被引:2,自引:0,他引:2
The nucleotide sequence of a new insertion sequence (IS) in Escherichia coli, IS421, was determined. It is 1340 bp long and contains inverted repeats of 22 bp at its termini. It is flanked by 13 bp direct repeats apparently generated upon insertion. There are two ORFs longer than 200 bp in IS421. One can encode a polypeptide of 371 amino acids (aa) and the other, which is on the other strand, can encode a polypeptide of 102 aa. The C-terminal part of the 371 aa polypeptide shows some homology to that of transposases encoded in some other known IS elements. The copy number of IS421 in chromosomal DNA was 4 for E. coli K-12 and B, and 5 for E. coli C, as determined by the Southern hybridization of restriction fragments. 相似文献
37.
X Wang N Sato M A Greer S E Greer S McAdams 《Biochemical and biophysical research communications》1989,163(1):471-475
The permeant molecules, urea and glycerol, evoked a prompt secretory burst of TSH and PRL when added to the extracellular medium of acutely dispersed anterior pituitary cells. Secretion of both hormones was proportional to the concentration of urea or glycerol between 26 and 104 mM (r greater than 0.89, P less than 0.001). Equivalent concentrations of the impermeant molecule, mannitol, did not induce secretion. The acute TSH and PRL secretory responses to TRH, hyposmolarity, and permeant molecules were qualitatively indistinguishable. These data support our hypothesis that cell swelling and resultant plasmalemma expansion is a potent inducer of hormone secretion. Since the secretory response to permeant molecules was not reduced in a Ca2+-free medium containing 0.1 mM EGTA, an increase in Ca2+ transport across the plasmalemma to raise cytosol Ca2+ concentration does not appear involved. 相似文献
38.
Mutagenesis of human granulocyte colony stimulating factor 总被引:9,自引:0,他引:9
T Kuga Y Komatsu M Yamasaki S Sekine H Miyaji T Nishi M Sato Y Yokoo M Asano M Okabe 《Biochemical and biophysical research communications》1989,159(1):103-111
To define the structure-function relationship, we have made a number of mutants of human granulocyte colony-stimulating factor (hG-CSF) by in vitro mutagenesis. The results indicate that most of the mutations located in the internal and C-terminal regions of the molecule abolished the activity, whereas the mutants without N-terminal 4, 5, 7, or 11 amino acids retained the activity. N-terminal amino acids were also altered by cassette mutagenesis using a synthetic oligonucleotide mixture. Among them, KW2228, in which Thr-1, Leu-3, Gly-4, Pro-5 and Cys-17 were respectively substituted with Ala, Thr, Tyr, Arg and Ser, showed more potent granulopoietic activity than that of intact hG-CSF both in vitro and in vivo. 相似文献
39.
The direct activation of human multidrug resistance gene (MDR1) by anticancer agents 总被引:10,自引:0,他引:10
K Kohno S Sato H Takano K Matsuo M Kuwano 《Biochemical and biophysical research communications》1989,165(3):1415-1421
Enhanced expression of a multidrug-resistance gene (MDR1) is observed in some cancer patient, but any regulatory mechanisms of MDR1 gene expression in this phenomenon is not yet known. In this study, the regulation of MDR1 gene was analysed by transient expression assays in the presence of anticancer agents. We found that MDR1 promoter could be activated directly on the addition of anticancer agents including vincristine, daunomycin, adriamycin and colchicine. The results suggest that the level of MDR1 mRNA expression is associated with previous chemotherapy, including drugs that select the multidrug resistance phenotype. 相似文献
40.