全文获取类型
收费全文 | 45445篇 |
免费 | 4291篇 |
国内免费 | 4626篇 |
出版年
2024年 | 28篇 |
2023年 | 538篇 |
2022年 | 620篇 |
2021年 | 1188篇 |
2020年 | 1252篇 |
2019年 | 1615篇 |
2018年 | 1429篇 |
2017年 | 1266篇 |
2016年 | 1381篇 |
2015年 | 1885篇 |
2014年 | 2447篇 |
2013年 | 3001篇 |
2012年 | 2423篇 |
2011年 | 2454篇 |
2010年 | 2068篇 |
2009年 | 2315篇 |
2008年 | 2578篇 |
2007年 | 2589篇 |
2006年 | 2559篇 |
2005年 | 2424篇 |
2004年 | 2280篇 |
2003年 | 2101篇 |
2002年 | 1962篇 |
2001年 | 1621篇 |
2000年 | 1211篇 |
1999年 | 1196篇 |
1998年 | 946篇 |
1997年 | 803篇 |
1996年 | 748篇 |
1995年 | 885篇 |
1994年 | 801篇 |
1993年 | 592篇 |
1992年 | 491篇 |
1991年 | 443篇 |
1990年 | 357篇 |
1989年 | 287篇 |
1988年 | 271篇 |
1987年 | 242篇 |
1986年 | 182篇 |
1985年 | 168篇 |
1984年 | 184篇 |
1983年 | 111篇 |
1982年 | 132篇 |
1981年 | 74篇 |
1980年 | 65篇 |
1979年 | 38篇 |
1978年 | 26篇 |
1977年 | 24篇 |
1976年 | 23篇 |
1974年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
In this article, we discuss molecular mechanisms involved in the evolution of amygdala kindling and the episodic loss of response
to pharmacological treatments during tolerance development. These phenomena allow us to consider how similar principles (in
different neurochemical systems) could account for illness progression, cyclicity, and drug tolerance in affective disorders.
We describe the phenomenon of amygdala-kindled seizures episodically breaking through effective daily pharmacotherapy with
carbamazepine and valproate, suggesting that these observations could reflect the balance of pathological vs compensatory
illness-induced changes in gene expression. Under certain circumstances, amygdala-kindled animals that were initially drug
responsive can develop highly individualized patterns of seizure breakthroughs progressing toward a complete loss of drug
efficacy. This initial drug efficacy may reflect the combination of drug-related exogenous neurochemical mechanisms and illness-induced
endogenous compensatory mechanisms. However, we postulate that when seizures are inhibited, the endogenous illness-induced
adaptations dissipate (the “time-off seizure” effect), leading to the re-emergence of seizures, a re-induction of a new, but
diminished, set of endogenous compensatory mechanisms, and a temporary period of renewed drug efficacy. As this pattern repeats,
an intermittent or cyclic response to the anticonvulsant treatment emerges, leading toward complete drug tolerance.
We also postulate that the cyclic pattern accelerates over time because of both the failure of robust illness-induced endogenous
adaptations to emerge and the progression in pathophysiological mechanisms (mediated by long-lasting changes in gene expression
and their downstream consequences) as a result of repeated occurrences of seizures. In this seizure model, this pattern can
be inhibited and drug responsivity can be temporarily reinstated by several manipulations, including lowering illness drive
(decreasing the stimulation current.), increasing drug dosage, switching to a new drug that does not show crosstolerance to
the original medication, or temporarily discontinuing treatment, allowing the illness to re-emerge in an unmedicated animal.
Each of these variables is discussed in relation to the potential relevance to the emergence, progression, and suppression
of individual patterns of episodic cyclicity in the recurrent affective disorders. A variety of clinical studies are outlined
that specifically test the hypotheses derived from this formulation. Data from animal studies suggest that illness cyclicity
can develop from the relative ratio between primary pathological processes and secondary endogenous adaptations (assisted
by exogenous medications). If this proposition is verified, it further suggests that illness cyclicity is inherent to the
neurobiological processes of episode emergence and amelioration, and one does not need to postulate a separate defect in the
biological clock. The formulation predicts that early and aggressive long-term interventions may be optimal in order to prevent
illness emergence and progression and its associated accumulating neurobiological, vulnerability factors. 相似文献
3.
Protein secretion in streptomycetes 总被引:1,自引:0,他引:1
4.
Lorenzo Alibardi 《Journal of morphology》2020,281(1):68-80
A highly upregulated gene during tail regeneration in lizards is Wnt2b, a gene broadly expressed during development. The present study examines the distribution of Wnt proteins, most likely wnt2b, by western blotting and immunofluorescence in the blastema-cone of lizards using a specific antibody produced against a lizard Wnt2b protein. Immunopositive bands at 48–50 and 18 kDa are present in the regenerative blastema, the latter likely as a degradation product. Immunofluorescence is mainly observed in the wound epidermis, including in the Apical Epidermal Peg where the protein appears localized in intermediate and differentiating keratinocytes. Labeling is more intense along the perimeter of keratinocytes, possibly as a secretory product, and indicates that the high epidermal proliferation of the regenerating epidermis is sustained by Wnt proteins. The regenerating spinal cord forms an ependymal tube within the blastema and shows immunolabeling especially in the cytoplasm of ependymal cells contacting the central canal where some secretion might occur. Also, regenerating nerves and proximal spinal ganglia innervating the regenerating blastema contain this signaling protein. In contrast, the blastema mesenchyme, muscles and cartilage show weak immunolabeling that tends to disappear in tissues located in more proximal regions, close to the original tail. However, a distal to proximal gradient of Wnt proteins was not detected. The present study supports the hypothesis that Wnt proteins, in particular Wnt2b, are secreted by the apical epidermis covering the blastema and released into the mesenchyme where they stimulate cell multiplication. 相似文献
5.
6.
7.
Conservation genetics considerations in fishery management 总被引:1,自引:0,他引:1
N. Ryman 《Journal of fish biology》1991,39(SA):211-224
8.
Mark A. Schembri Alan A. Woods Ronald C. Bayly John K. Davies 《FEMS microbiology letters》1995,133(3):277-283
Abstract Transferrin-binding proteins from Neisseria meningitidis vary among different isolates. We have identified and studied a hypervariable region adjacent to the carboxyl-end of the transferrin-binding domain of the Tbp2 molecule. The tbp2 genes from six strains of N. meningitidis were cloned and sequenced in this particular region. Sequence analysis of these regions along with five other sequences available from pathogenic Neisseria showed a common organisation of seven highly variable nucleotide stretches interspersed with six conserved nucleotide stretches. The variable regions correlated with the location of immunoreactive epitopes in polyclonal antisera raised to transferrin-binding proteins identified by peptide pin technology. Sequence analysis suggested a mosaic-like organisation of the tbp2 genes. Taken together, these data suggest that the antigenic variation in this part of the protein may result from a strong host immune pressure. 相似文献
9.
Jiefeng He Haichao Zhao Dongfeng Deng Yadong Wang Xiao Zhang Haoliang Zhao Zongquan Xu 《Journal of cellular physiology》2020,235(3):2464-2477
This study aimed to identify significant biomarkers related to the prognosis of liver cancer using long noncoding RNA (lncRNA)-associated competing endogenous RNAs (ceRNAs) analysis. Differentially expressed mRNA and lncRNAs between liver cancer and paracancerous tissues were screened, and the functions of these mRNAs were predicted by gene ontology and pathway enrichment analyses. A ceRNA network consisting of differentially expressed mRNAs and lncRNAs was constructed. LncRNA FENDRR and lncRNA HAND2-AS1 were hub nodes in the ceRNA network. A risk score assessment model consisting of eight genes (PDE2A, ESR1, FBLN5, ALDH8A1, AKR1D1, EHHADH, ADRA1A, and GNE) associated with prognosis were developed. Multivariate Cox regression suggested that both pathologic_T and risk group could be regarded as independent prognostic factors. Furthermore, a nomogram model consisting of pathologic_T and risk group showed a good prediction ability for predicting the survival rate of liver cancer patients. The nomogram model consisting of pathologic_T and a risk score assessment model could be regarded as an independent factor for predicting prognosis of liver cancer. 相似文献
10.
Gary L Bratthauer Markku Miettinen Fattaneh A Tavassoli 《The journal of histochemistry and cytochemistry》2003,51(11):1527-1531
Eighteen commercially available antibodies reactive against different cytokeratin proteins were tested on classic examples of lobular intraepithelial neoplasia (LIN) and of ductal intraepithelial neoplasia (DIN) of the breast. About 90% of higher-grade DIN (AIDH and DCIS) show no or substantially diminished reaction with clone 34betaE12 (specified as reactive against keratins 1, 5, 10, and 14 as determined by the manufacturer), while the cells of LIN were found to express the antigen reactive with this antibody. To determine which of these four keratins are present in the cells of LIN, antibodies reactive against these individual four keratins were tested. None of the four antibodies to keratins 1, 5, 10, or 14 reacted with the cells of LIN. To investigate this further, 13 additional monoclonal antibodies to various other keratin proteins were tested on the cells of LIN. Those that successfully reacted with the cells of LIN were further tested on the cells of DIN. All of the individual antibodies reactive with the cells of LIN were also reactive with the cells of DIN to a degree, with clone RCK108 (reactive against keratin 19) coming the closest to demonstrating the reactivity seen with 34betaE12. We conclude that the reactivity seen in the cells of LIN with 34betaE12 is due to either (a) a crossreaction with keratin 19 that is slightly less prominent than the reaction of the individual clone RCK108, (b) a crossreaction with a keratin protein that was not tested (3, 11, 12), (c) a crossreaction with a protein closely resembling keratin in formalin-fixed, paraffin-embedded tissue, or (d) the detection of a mutated or truncated form of keratin 1, 5, 10, or 14 that cannot be detected by the individual monoclonal antibody. 相似文献