全文获取类型
收费全文 | 12403篇 |
免费 | 660篇 |
国内免费 | 673篇 |
出版年
2024年 | 13篇 |
2023年 | 163篇 |
2022年 | 229篇 |
2021年 | 305篇 |
2020年 | 309篇 |
2019年 | 348篇 |
2018年 | 379篇 |
2017年 | 239篇 |
2016年 | 284篇 |
2015年 | 383篇 |
2014年 | 573篇 |
2013年 | 745篇 |
2012年 | 437篇 |
2011年 | 663篇 |
2010年 | 528篇 |
2009年 | 718篇 |
2008年 | 699篇 |
2007年 | 693篇 |
2006年 | 668篇 |
2005年 | 632篇 |
2004年 | 551篇 |
2003年 | 452篇 |
2002年 | 421篇 |
2001年 | 316篇 |
2000年 | 256篇 |
1999年 | 263篇 |
1998年 | 222篇 |
1997年 | 214篇 |
1996年 | 188篇 |
1995年 | 185篇 |
1994年 | 194篇 |
1993年 | 157篇 |
1992年 | 142篇 |
1991年 | 116篇 |
1990年 | 114篇 |
1989年 | 109篇 |
1988年 | 75篇 |
1987年 | 67篇 |
1986年 | 57篇 |
1985年 | 76篇 |
1984年 | 114篇 |
1983年 | 88篇 |
1982年 | 88篇 |
1981年 | 62篇 |
1980年 | 57篇 |
1979年 | 40篇 |
1978年 | 22篇 |
1977年 | 26篇 |
1976年 | 14篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Peter Bräunig 《Cell and tissue research》1990,260(1):95-108
Summary The nervus corporis cardiaci III (NCC III) of the locust Locust migratoria was investigated with intracellular and extracellular cobalt staining techniques in order to elucidate the morphology of neurons within the suboesophageal ganglion, which send axons into this nerve. Six neurons have many features in common with the dorsal, unpaired, median (DUM) neurons of thoracic and abdominal ganglia. Three other cells have cell bodies contralateral to their axons (contralateral neuron 1–3; CN 1–3). Two of these neurons (CN2 and CN3) appear to degenerate after imaginal ecdysis. CN3 innervates pharyngeal dilator muscles via its anterior axon in the NCC III, and a neck muscle via an additional posterior axon within the intersegmental nerve between the suboesophageal and prothoracic ganglia. A large cell with a ventral posterior cell body is located close to the sagittal plane of the ganglion (ventral, posterior, median neuron; VPMN). Staining of the NCC III towards the periphery reveals that the branching pattern of this nerve is extremely variable. It innervates the retrocerebral glandular complex, the antennal heart and pharyngeal dilator muscles, and has a connection to the frontal ganglion.Abbreviations
AH
antennal heart
-
AN
antennal nerves
-
AO
aorta
-
AV
antennal vessel
-
CA
corpus allatum
-
CC
corpus cardiacum
-
CN1, CN2, CN3
contralateral neuron 1–3
-
DIT
dorsal intermediate tract
-
DMT
dorsal median tract
-
DUM
dorsal, unpaired, median
-
FC
frontal connective
-
FG
frontal ganglion
-
HG
hypocerebral ganglion
-
LDT
lateral dorsal tract
-
LMN, LSN
labral motor and sensory nerves
-
LN+FC
common root of labral nerves and frontal connective
-
LO
lateral ocellus
-
MDT
median dorsal tract
-
MDVR
ventral root of mandibular nerve
-
MVT
median ventral tract
-
NCA I, II
nervus corporis allati I, II
-
NCC I, II, III
nervus corporis cardiaci I, III
-
NR
nervus recurrens
-
NTD
nervus tegumentarius dorsalis
-
N8
nerve 8 of SOG
-
OE
oesophagus
-
OEN
oesophageal nerve
-
PH
pharynx
-
SOG
suboesophageal ganglion
-
T
tentorium
-
TVN
tritocerebral ventral nerve
-
VLT
ventral lateral tract
-
VIT
ventral intermediate tract
-
VMT
ventral median tract
-
VPMN
ventral, posterior, median neuron
-
1–7
peripheral nerves of the SOG
-
36, 37, 40–45
pharyngeal dilator muscles 相似文献
42.
Efficient integrative transformation of the phytopathogenic fungus Alternaria alternata mediated by the repetitive rDNA sequences 总被引:4,自引:0,他引:4
An attempt was made to transform Alternaria alternata protoplasts using a plasmid vector, pDH25, bearing the Escherichia coli hygromycin B (Hy) phosphotransferase gene (hph) under the control of the Aspergillus nidulans trpC promoter. Transformants arose on a selective medium containing 100 μg Hy/ml. There were two types of transformants, forming large and small colonies on the selective medium. Transformation with one μg of the vector produced an average of 4.5 large colonies and 600 small ones. In large-colony transformants, the vector often integrated into the recipient chromosome in the form of highly rearranged tandem arrays. To increase transformation efficiency, fragments of the highly repetitive ribosomal RNA gene cluster (rDNA) of A. alternata were used to construct four new vectors for homologous recombination system. Use of these vectors gave higher transformation efficiency than the original plasmid. The best vector, pDH25r1a, gave rise to large-colony transformants at a frequency 20 times higher than pDH25. Transformation events in A. alternata with pDH25r1a occured by homologous recombination as a single crossover between the plasmid-borne rDNA segment and its homologue in the chromosome, often giving rise to tandemly repeated vector DNA. 相似文献
43.
Garry J. Smith Heinz W. Kunz Harold A. Dunsford Thomas J. Gill III 《Cell biology and toxicology》1990,6(2):205-217
The histopathological response and cell culture characteristics of liver cells from the R16 (grc
–) strain of rats, which carries an MHC-linked deletion, were examined one week after a single intraperitoneal injection of 200 mg/ kg body weight diethylnitrosamine (DEN) and were compared with the response of liver cells from wild type (grc+) rats. The DEN exposure induced hydropicl vacuolar changes in the parenchymal cells and a limited proliferation of oval cells in the periportal areas of the livers of both grc+ and grc rats. Primary culture of collagenase-digested livers consisted of parenchymal, bile ductular and oval-related cells as determined by cell-specific immunohistochemistry. Subpassaged cells from grc+ rats exhibited oval cell ultrastructural morphology, inducible histochemical staining for gammaglutamyl transpeptidase (GGT), and DEN-associated onset of anchorage-independent growth. Primary cultures of liver cells from R16 rats consistently failed to form cell strains upon subpassage.Abbreviations DEN
diethylnitrosamine
-
grc
growth and reproduction complex
- GGT
gamma-glutamyl transpeptidase
- MHC
major histocompatibility complex 相似文献
44.
Alessandra Faraoni Roberto Santucci Luigi Campanella Gloria Tranchida Maurizio Brunori 《Biometals》1990,3(2):122-124
Summary The electrochemical behaviour of Fe(III)-protoporphyrin IX entrapped into a cellulose triacetate membrane has been investigated by cyclic voltammetry. The physical entrapment into a solid matrix does not modify the redox properties of the entrapped berries, which also act as efficient promoters in the electrochemistry of cytochromec. Such a system represents a promising example of a simple solid-state promoter, and stimulates further investigations in order to obtain more complex systems that may be of significance for basic and applied bioelectrochemistry. 相似文献
45.
A total of 627 cattle representing seven breeds from south central Nebraska, USA were tested for 37 BoLA antigens which behave as products of 37 distinct alleles of the class I BoLA-A locus. Four antigens were absent from all breeds tested. The other antigens showed marked and statistically significant differences in breed distribution. There was no evidence for blank (null) alleles. The number of alleles in each breed ranged from 10 to 20. The Hereford and Simmental populations tested were less polymorphic than the Angus, Brown Swiss, Charolais, Gelbvieh and Limousin populations. 相似文献
46.
Rafael Cantera 《Cell and tissue research》1988,253(2):425-433
Summary The presence and distribution of neurons immunoreactive against antibodies to serotonin (5-HT) and gastrin/cholecystokinin (gastrin/CCK) has been studied in the larval retrocerebral complex of the blowfly Calliphora erythrocephala, a composite structure which consists of the corpus cardiacum, the corpus allatum, the thoracic gland and a portion of the cephalic aorta. Immunoreactive material was found in all these elements except in the corpus allatum. Six to eight cell bodies in the corpus cardiacum and four to eight cell bodies in the thoracic gland were 5-HT immunoreactive (5-HTi). These 5-HTi cell bodies send processes to the neuropil of the corpus cardiacum and to neurohemal sites in the cephalic aorta, corpus cardiacum and ventral part of the thoracic gland. Six to eight cell bodies in the corpus cardiacum and four to six cell bodies in the thoracic gland reacted with antibodies against gastrin/CCK. These cell bodies send processes to the neuropil of the corpus cardiacum and to neurohemal sites in the corpus cardiacum and the cephalic aorta in a pattern resembling that of the 5-HTi fibers. Additional gastrin/CCK-like immunoreactive fibers were shown to come from the central nervous system via the two nervi corporis cardiaci. An electron-microscopical analysis was performed to analyze further the morphological features revealed by the light-microscopic immunocytochemical technique. This confirmed the existence of neurosecretory-like terminals among the gland cells of the thoracic glands and the existence of neurohemal sites in several regions of the larval retrocerebral complex. Some functional aspects of the retrocerebral complex are discussed on the basis of the presented data. 相似文献
47.
Uno Lindberg Clarence E. Schutt Eva Hellsten Ann-Christine Tjder Thomas Hult 《Biochimica et Biophysica Acta (BBA)/General Subjects》1988,967(3)
In the purification of proline hydroxylase by affinity chromatography on poly(L-proline)-Sepharose it was found earlier that two other components, profilin and the complex profilin-actin, also bind with high affinity to this matrix. We have exploited this observation to develop a rapid procedure for the isolation of profilin and profilin-actin complexes in high yields directly from high-speed supernatants of crude tissue-extracts. Through an extensive search for elution conditions, avoiding poly(L-proline) as the desorbant, we have found that active proteins can be recovered from the affinity column with a buffer containing 30% dimethyl sulphoxide. Subsequent chromatography on hydroxylapatite separates free profilin and the two isoforms of profilactin, profilin-actinβ and profilin-actinγ. The profilin-actin complexes produced this way have high specific activities in the DNAase-inhibition assay, give rise to filaments on addition of Mg2+, and can be crystallized. From the isolated profilin-actin complexes the β- and γ-actin isoforms of non-muscle cells can easily be prepared in a polymerization competent form. Pure profilin is either obtained from an excess pool present in some extracts or by dissociation of profilin-actin complexes and removal of the actin. 相似文献
48.
Abstract Four plasmids were constructed by associating Escherichia coli and yeast selection markers and replication origins to a structural gene coding for aminoglycoside phosphotransferase (APH(3')) controlled by different flanking sequences. We used the two bacterial genes of Tn5 (APH(3')II) and Tn903 (APH(3')I) as such and the chimeric pSVneo (APH(3')II) and pNOSneo (APH(3')II) constructs, functional in mammalian and plant cells, respectively. Yeast clones resistant to G418 were obtained with all plasmids except with that bearing the bacterial APH(3')II gene. The three plasmids harbouring the functional APH genes, however, conferred different levels of G418 resistance to yeast. 相似文献
49.
An extensive analysis of genomic DNA preparations from a number of normal and malignant tissues revealed BglII site polymorphism of the human p53 gene. Approximately 10% of p53 gene alleles were found to contain an additional BglII site localized in a region of intron I. This allelic form of p53 gene was also responsible for p53 protein having altered electrophoretic mobility. Molecular cloning and sequencing of both the alleles of p53 gene revealed a base-pair change in codon 72 causing arginine → proline substitution in the allele with the additional BglII site. Both variants of the p53 gene may occur in homozygous state and are therefore functional. 相似文献
50.